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THE SOIL SOLUTION 



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The Soil Solution 



The Nutrient Medium for Plant Growth 



By 



FRANK K. CAMERON 

In Charge, Physical and Chemical Investigations, Bureau of Soils, 
U. S. Department of Agriculture 



EASTON. PA.: 

THE CHEMICAL PUBLISHING CO. 
1911 



LONDON, ENGLAND: 

WILLIAMS & NORGATE 

14 HENRIETTA STREET, COVENT GARDEN, W- C. 



Copyright, 191 r, by Edward Hart 






Preface. 

It has long been the custom to regard soil chemistry from 
one of two diametrically opposed points of view. Either, it has 
been considered extremely simple, or complex and hopelessly 
difficult. In either case the impression has generally prevailed 
that practical work in soil chemistry consists in treating the 
soil with some solvent or other and analyzing the resulting solu- 
tion for "available" plant food elements ; in oiher words, that 
the chemist's role in soil studies is merely that of an analyst. 

Soil chemistry is complex, but not by any means hopelessly 
so. Unfortunately, the complexity of most of the problems 
presented has deterred the student of pure chemistry from attack- 
ing them, and because they do not offer any material pecuniary 
rewards, they have not appealed strongly to the investigator in 
applied chemistry. Investigations in soil chemistry, for their 
own sake, or for the sole purpose of increasing the sum total 
of human knowledge concerning the phenomena taking place in 
the soil, have been comparatively rare. The subject has general- 
ly been regarded from the analytical point of view and as inci- 
dental to agronomic studies. 

One purpose of this little book is to show the investigator in 
chemistry who is not limited by the condition that his work must 
bring some personal financial return, that the soil and its pro- 
blems offer a field for his efforts quite worthy of ranking along- 
side the mO'St interesting branches of pure chemistry, as well as 
being of the very highest importance to the development of the 
welfare of the human race. Another purpose is to point out 
the line of attack upon the problems of soil chemistry which at 
this time offers the largest opportunity for results. In how far 
the details of the story in the following pages are correct, time 
with its further investigations will tell. In a sense, the correct- 
ness of the details is of secondary importance. It is of the first 
importance, however, that there should be a general recogni- 
tion that soil phenomena are essentially dynamic in character, 
and that the investigation of the properties of the soil solution 
and its relation to crop production is a procedure certain to 
yield results of positive value. 



IV PRKFACE 

Again, it is a purpose of this book to make available for 
students of agriculture, a systematic outline of the work so far 
accomplished in this particular field. It is to the students of to- 
day from whom are to come the investigations of the near 
future that the book is particularly addressed. Some of the 
details presented in the following pages are matters on which 
opposed opinions are now held strongly by different authorities, 
and to the unbiased minds of the coming investigators must be 
left the decision as to how closely the truth has been approxi- 
mated in what is written to-day. The field of effort covered 
by this book is one in which there is an increasing activity, and 
new facts and deductions will inevitably bring modifications 
to present opinions. To encourage this further acquisition of 
knowledge is the main purpose of the book. 

The material brought together in this book has been presented 
to the faculties and students of several of our Agricultural 
Colleges, in the form of a short course of lectures. In large 
part, moreover, it has been published in X^olume XIV of the 
Journal of Physical Chemistry. To make it accessible to and 
more easily read by one familiar with the progress of technical 
soil investigations, it has been recast in its present form. 

It has been assumed that the reader will have a fair working 
knowledge of the concepts of modern chemistry. Nevertheless, 
an effort has been made to avoid technical terms so far as this 
can be done without undue sacrifice of lucidity of expression. 
Free references have been made to the bulletins of the Bureau 
of Soils, U. S. Department of Agriculture, because they are 
generally accessible to the American student, and because in 
them' w'ill be found detailed discussions and bibliographical 
material pertinent to the subjects outlined here. To his coworkers, 
the author is indebted for many criticisms and suggestions ; and 
more especially in the making of the book is he indebted to 
Mr. S. C. Stuntz. 

Washington, D. C. 
1911. 



Table of Contents. 



PAGE 

, . iii 



Preface 

I. The Soil 

II. Soil Management or Control 4 

III. Soil Analysis and the Historical Methods of Soil Investigation ... b 

IV. The Plant-Food Theorj- of Fertilizers ^ ^ 

V. The Dynamic Nature of Soil Phenomena ^^ 

VI. The Film Water ; ^^ 

VII. The Mineral Constituents of the Soil Solution 3i 

VIII. Absorption by Soils ^9 

IX The Relation of Plant Growth to Concentration 7° 

X. The Balance Between Supply and Removal of Mineral Plant ^ 

Nutrients... "^ 

XI. The Organic Constituents of the Soil Solution 79 

XII. Fertilizers ^°^ 

., ,. no 

XIII. Alkah 

, , 127 

Index 



AN INTRODUCTION TO THE STUDY OF 
THE SOIL SOLUTION. 



Chapter I. 

THE SOIL. ' 

The soil, or that part of the land surface of the earth 
adapted to the growth and support of crops, is a heterogeneous 
mixture composed of solids, gases and a liquid, and containing 
living organisms. There are present: mineral debris from rock 
degradation and decomposition; organic matter from the de- 
gradation and decomposition of former plant and animal tissues ; 
the soil atmosphere, always richer in carbon dioxide and water 
vapor and possibly other gases than the atmosphere above the 
soil; living organisms, such as various kinds of bacteria and 
fungi, with the products of their activities, notably the ''nitrogen 
carriers" and the enzymes ; and finally the soil moisture, a solu- 
tion of products yielded by the above components and in equili- 
brium or approaching equilibrium with the solids and gases with 
which it is in contact. 

In its relation to crop plants,^ that part of the soil of im- 
mediate importance is the soil moisture. From this solution 
the plants, through their roots, draw all the material involved 
in their growth, except the carbon dioxide absorbed through 
their leaves. The soil solution is the natural nutrient medium 
from which the plants absorb the mineral constituents which 
have been shown to be absolutely essential to their continued 
existence and development. And from this solution plants some- 
times absorb dissolved organic substances, but such absorptions 
are probably adventitious and incidental to the growth of the 
plant in a particular environment. While it appears certain 

^ By crop plants are meant the ordinary green plants employed in 
agriculture. As is well-known, the fungi as well as certain parasitic and 
saprophytic non-green seed plants obtain their nutriment in a very differ- 
ent way from ordinary green crop plants. 



2 THE SOIL SOLUTION 

that no organic substance in the nutrient medium is necessary to 
the maintenance of plant growth, nevertheless organic sub- 
stances are probably always present under natural conditions. 
They may or may not be absorbed by the plant and may affect 
it beneficially or otherwise. 

The study of the soil solution is of the first importance in the 
investigation of the relation of the soil to plant growth, and in 
the following pages there is given an outline of our present 
knowledge of the chemical principles involved, with such dis- 
cussion of the physical and biological factors as is essential to 
an orderly presentation of the subject. 

To understand clearly the relations of the soil solution to the 
soil as a whole and to the plant which it nourishes, it is desir- 
able to consider some attributes of soils in general. Every soil, 
no matter of wdiat type it may be, is a complex system. In it 
various processes are continually in operation, excepting possibly 
in the extreme case when it remains frozen for a time at some 
definite temperature. The resultant or summation of these pro- 
cesses, whether expressed in plant production or otherwise, will 
vary from time to time, both quantitatively and in direction ; 
for instance, as to the amount and kinds of plant growth it pro- 
duces. That is to say, any particular soil area is seemingly an 
organic entity, functioning according to its own inherent pro- 
perties, but subject to the modifying influences of environment, 
as by exceptional climatic extremes, flood, fire, and especially 
by artificially imposed agencies of control. 

From the practical point of view the problem of the soil 
in its relation to crop production is like the problem of the 
factory or of any other industrial endeavor, in that it is a 
problem of management or control. The soil possesses this dis- 
tinction, however, that it is both the raw material and the 
factory.^ The processes involved are physical, chemical and 

According to S. W. Johnson — Some points of agricultural science. 
Am. Jour. Sci. (2), 28, 71-85 (1859) — "The soil (speaking in the widest 
sense) is then not only the ultimate exhaustless source of mineral (fixed) 
food, to vegetation, but it is the storehouse and conservatory of this 
food, protecting its own resources from waste and from too rapid use. 
and converting the highly soluble matters of animal exuviae as well as of 
artificial refuse (manures) into permanent supplies." 



the; soil. 3 

biological, are always numerous and interdependent, and are 
never (speaking generally) exactly the same, so that each soil 
possesses marked individuality. No matter how soils may be 
classified, as for instance into provinces, series and types, ^ the 
fact remains that the soil of the individual field has properties 
which give it a crop-producing pow'er, an adaptation to a specific 
crop or crop rotation, or a responsiveness to cultural treatment, 
which can not be anticipated in any other field. Consequently, 
there is no possibility of reducing soil management or agriculture 
to the state of an exact science. That is to say, scientific 
investigation of the problems involved cannot be expected to 
yield absolute results, although furnishing the best possible basis 
on which to form judgments. Soil management, like other 
agricultural practices, is an art, more or less well founded on 
scientific principles, perhaps, but susceptible of much higher 
development as the scientific principles involved become better 
understood. 

^ For definitions, see Soil Survey Field Book, 1906, Bureau of Soils, 
U. S. Dept. of Agriculture, pp. 15-24. On the ground that experience 
has shown that genetic classifications are the ones which have generally- 
persisted and proved the most useful, objection might be made to the 
classification just cited. But a careful inspection of the results of the 
Soil Survey by the U. S. Department of Agriculture will show that while 
not categorically stating the fact, to all intents and purposes it has 
employed a genetic classification. This is exemplified by the fact that its 
delineation of soil provinces corresponds quite closely with the recognized 
physiographic provinces of the United States. See map accompanying 
Soils of the United States, by Milton Whitney, Bull. No. 55, Bureau of 
Soils, U. S. Dept. Agriculture, 1909. 



Chapter 11. 

SOIL MANAGEMENT OR CONTROL. 

Aside from such devices as greenliouses, wind-breaks, etc., 
which have a local application only, there are three general 
methods of soil control : tillage methods, such as plowing and 
harrowing ; rotation of crops ; and the use of soil amendments 
or "fertilizers." 

The existing knowledge regarding tillage methods is generally 
considered to be fairly satisfactory. The purposes are well 
understood, namely, to break up and "fine'' the soil/ to keep 
down weeds, and by forming mulches to decrease the loss of 
water by evaporation. Not much increase is being made in our 
theoretical knowledge of this subject, although mechanical im- 
provements in the implements of tillage are being and will un- 
doubtedly continue to be made. 

The existing knowledge concerning crop rotations is fairly 
extensive, but it is almost entirely empirical. Some at least of 
the purposes served by a rotation of crops are fairly well known, 
such as the elimination of weeds or lower types of parasitic 
growth associated with particular crops ; the introduction of 
humus by a grass crop or a green manure crop, especially by the 
Lcgiiminosae with their symbiotic Asobacteria; the improve- 
ment in the structure or arrangement of the soil particles by 
alternating deep-rooted and shallow-rooted crops ; the avoidance 
of continually growing a crop in the presence of its own excreta, 
products of decay, etc. ; and lastly, economic and market con- 
siderations. 

The existing knowledge of fertilizers, in spite of a vast amount 

of work and an enormous literature, is still very meagre and it 

also is almost entirely empirical ; and this because studies on the 

subject have been dominated for three-quarters of a century 

by one theory almost to the exclusion of any other. The 

exponents of this theory have generally assumed that the action 

1 Actually, to granulate the soil. "Fine" would seem to be a mis- 
nomer, but its agricultural significance is well understood, and it has the 
sanction of long usage in the literature. 



SOIIv MANAGEMENT OR CONTROL 5 

of fertilizers is on the plant rather than on the soil, and is 
independent of other factors. That is, while it is admitted that 
other factors influence plant growth, it has been held that the 
effect of the fertilizer is not to modify the influence of the other 
factors but to directly influence the plant by increasing its food 
supply. As a consequence, it has also been generally assumed 
that the influence of fertilizers is additive, that is, the increase 
in yield of crop is proportional to the increase in fertilizer added, 
and the increase in yield produced by adding two fertilizers is 
the sum of the increases which would have been produced by 
each alone. In this form the theory is essentially a quantitative 
one, and fertilizer practice should be easily susceptible of con- 
trol by chemical analyses. But the large mass of data obtained 
from plot experiments shows that fertilizer effects are not 
additive. Indeed, the addition of some one or more fertilizer 
constituent is sometimes followed by a decreased yield. For 
example, about 20 per cent, of the trials of fertilizers on soils 
growing corn and reported by the American State Experiment 
Stations show a decreased yield. And furthermore, in spite of 
the quantitative character of the theory, and the numerous 
analyses of soils and of plants which have been made, there is yet 
lacking any authoritative method for determining in quantitative 
terms the fertilizer needs of a soil. That analytical methods 
have a very restricted value in indicating even qualitatively the 
fertilizer needs of the soil is evidenced by the fact that within 
the past few years a number of the State Experiment Stations 
have publicly announced their unwillingness to undertake them.^ 

^ In this connection see : The texture of the soil, by L. H. Bailey, 
Cornell University Agr. Expt. Sta., Bull. No. 119, (1896) ; Suggestions 
regarding the examination of lands, by E. W. Hilgard, University of 
California, College of Agriculture, Circ. No. 25^ (1906) ; Chemical analy- 
sis of soils, by William P. Brooks, Massachusetts Agr. Expt. Sta. Circ. 
No. II, (1907) ; Testing soils for fertilizer needs, by F. W. Taylor, New 
Hampshire Agr. Expt. Sta., Circ. No. 2^ (1908) : The uses and limitations 
of soil analysis, by J. T. \\'illard, The Industrialist, Kansas State Agri- 
cultural College, 34, 291, (1908) ; Soil analysis, by Wm. Frear, Pennsyl- 
vania Agr. Expt. Sta., Chem. Circ. No. i ; How to determine the ferti- 
lizer requirements oi Ohio soils, by Chas. E. Thorne, Ohio Agr. Expt. 
Sta., Circ. No. 79» (1908) ; Concerning work which the station can and 
cannot undertake for residents of the state, by Joseph L. Hills, Vermont 
Agr. Expt. Sta., Circ. No. 3, (1909). 



6 THE SOIL SOLUTION 

The common procedure has been to define some arbitrary 
percentage hmit in the soil, below which the soil is supposed to 
require fertilizers. But the amount of fertilizer to be applied is 
suggested on the indefinite basis of "experience." Thus, Hil- 
gard, in an mteresting discussion of this subject/ quotes Dyer 
as showing that "on Rothamsted soils of known productiveness 
or manurial condition, it appears that when the citric acid ex- 
traction yields as much as 0.005 per cent, of potash and o.oio per 
cent, of i)hosphoric acid, the supply is adequate for normal crop 
production, so that the use of the above substances as fertilizers 
would be, if not inefifective, at least not a profitable investment." 
Hilgard himself sets limits as determined by strong hydrochloric 
acid digestion ; thus a soil containing upwards of 0.45 per cent. 
(KoO) does not need this substance as a fertilizer, wdiile one con- 
taining below 0.25 per cent, does need it at once, and inter- 
mediate percentages indicate that potash fertilizers would prob- 
ably be profitable : the corresponding upper and lower limits for 
phosphoric acid are set at o.io per cent, and 0.05 per cent. 
But Hilgard ])oints out that various things, such as the content 
of lime, or the texture of the soil, may materially alter these 
limits. In a very interesting set of experiments in which white 
mustard was grown in various soils, and these same soils diluted 
with various amounts of dune sand which had previously been 
extracted with strong hydrochloric acid, he found that the plants 
did best when the soils had been diluted with four times their 
weight of the extracted sand. This was the case even with a 
pulverulent sandy loam ; and with a black adobe, the best results 
were obtained when the diluted soil contained but 0.15 per cent. 
potash (KoO) and 0.04 per cent, phosphoric acid (PoOr,). It 
also appears that Hilgard regards soil analyses of value only in 
the case of virgin soils or soils which have been out of cultivation, 
and in common with other authorities, he fails to jXDint out how to 
determine the amount of fertilizer needed by lands. 

It is clear, therefore, that the principles underlying the practice 
or art of soil management and crop rotation are in a state of 

* Soils by E. W. Hilgard, 1906, p. 339, ct seq. 



SOIL MANAGEMENT OR CONTROL 7 

development, far from satisfactory, and scientific methods of soil 
control yet wanting/ Recent activities in soil investigations, 
however, justify the hope that much improvement is to be 
anticipated, and the application of the modern methods of physi- 
cal, chemical, and biological research to the soil problem promises 
a sure and probably rapid advance in this branch of applied 
science. 

^ It should, of course, be borne in mind that soil factors are not the 
only ones in crop production. Control by seed selection, breeding of 
standard types of plants, etc., may be. and probably is, more highly de- 
veloped than control by soil factors. The same might possibly be claimed 
for moisture supply in irrigated areas ; but on the other hand, such fac- 
tors as the bacterial and lower life processes in the soil are generally 
under little or no control, and as a rule the amount and distribution of 
sunlight under none at all. A notable effort has been made in the last 
case with shade-grown tobacco (see Bulletins Nos. 20 and 39, Bureau 
of Soils, U. S. Dept. Agriculture) and a few cases are known where 
shade-crops are employed, but not in general agriculture. 



Chapter III. 

SOIL ANALYSIS AND THE HISTORICAL METHODS 
OF SOIL INVESTIGATION. 

Owing to the labors of Davy, Boussing-ault, de Saussure, 
Liebig, Sachs, Knop, Sahii-Horstmar, and other scarcely less 
distinguished savants, it has been clearly shown that growing 
plants need certain mineral elements in order to maintain their 
metabolic functions, and that these mineral elements can be ob- 
tained, under normal conditions, from the soil. All subsequent 
investigation has confirmed these statements and they can now 
be accepted as facts with as much assurance as any known law of 
nature. 

The determination and formulation of these two fundamental 
facts came at a time when analytical chemistry was being rapidly 
developed and was finding w'ide and useful applications in numer- 
ous fields of activity. It was natural, therefore, that analytical 
chemistry should be enlisted in this new field of work, obviously 
of the first importance to the welfare of mankind. It was early 
found, however, that the chemical analysis of a soil fails to ex- 
plain its relative productivity. In other words the content of a 
soil with respect to potash, phosphoric acid, or other mineral 
plant-food constituent, bears no necessary relation to its crop- 
producing power. Many cases were found where one soil 
"analyzed well' but did not produce as large a crop as another 
soil which "analyzed poor."^ To meet this difficulty a subsidiary 
hypothesis was brought forward, which rapidly gained general 
acceptance although lacking experimental support. 

This hypothesis supposes that the mineral constituents of the 
soil are present in two different chemical conditions or distinct 
kinds of combinations, one of which readily gives up its con- 
stituents to growing plants, while the other does not ; and the 
constituents have, therefore, been called respectively "available" 

* See also, Die Aufnahme cler Xahrstoffe aus dem Bcden durch die 
Pflanzen, von J. Konig und E. Haselhoff, Landw. Jahrh., 23, 1009, 1030, 
(1894). 



SOIIv ANAIvYSIS AND INVESTIGATION 9 

and "non-available." It would appear from his writings that 
Liebig regarded this distinction as applying to the "absorbed" 
or "adsorbed" mineral matter; that is, on the one hand the 
material held in or upon the soil grains by surface forces, and on 
the other the chemically combined constituents in the minerals 
themselves. We know that Liebig was much impressed by the 
absorption experiments of Way, and himself did much work in 
this field. ^ But the great body of soil investigators has evident- 
ly held to the opinion that there are two general classes of 
minerals in the soil. Some have held that the "available" 
potassium is held in zeolites or "zeolitic" minerals, an interesting 
example often cited being glauconite or "green sand marl," 
which sometimes contains phosphorus as well as potassium ;- 
in minerals which are easily broken down by alkaline solutions, 
as by sodium carbonate solutions or ammonia; or in minerals 
which are easily broken down by organic acids supposedly ex- 
creted from the roots of growing plants, or formed by the decay 
of plant tissue.^ 

With the advent of this idea of a distinction between the 
available and non-available mineral plant-food elements in the 
soil, came attempts to distinguish them by analytical methods. 
Of these attempts we now have a bewildering array, most of 

* Way was misled, as we now know, in considering the results of his 
absorption experiments with soils as merely metathetical reactions; see 
Absorption by soils, by Harrison E. Patten and William H. Waggaman, 
Bull. No. 52, Bureau of Soils, U. S. Dept. Agriculture, 1908. 

^The formation of zeolites in the soil has often been assumed, but 
has not yet been pro.ven ; see Rocks, rock-weathering and soils, by George 
P. Merrill, 1906, p. 363. 

^ The classic experiments of Sachs, in producing etchings on marble 
slabs, and the etchings observed occasionally on rock surfaces are the 
proofs universally cited. The experiments of Czapek, who substituted 
slabs of aluminum phosphate and other substances for the marble, and 
those of Ko'Ssowitch, show that the action can be accounted for more 
satisfactorily and reasonably as due to dissolved carbon dioxide. In fact 
such etchings can be produced on marble slabs by laying platinum wires 
upon them and covering with moist soil, or cotton, or mats of filter- 
paper; see Bull. No. 22, p. 14, and Bull. No. 30, p. 41, Bureau of Soils, 
U. S. Dept. Agriculture. 



10 THE SOIIv SOLUTION 

thcni frankly empirical. For instance, Ililgard, in his classical 
investigation of the cotton soils for the Tenth Census, treated 
his soil samples with an excess of hydrochloric acid, evaporated 
to diyness, extracted with water, and regarded the extracted 
mineral constituents as available. In Germany, a method similar 
to Hilgard's is now in common use, while in France nitric acid is 
preferred generally because it is supposed to have peculiar sol- 
vent powers on soil phosphates. In the United States the "offi- 
cial method" of the Association of Official Agricultural Chemists 
is to keep lO grams of the soil in contact with lOO cc. of a solu- 
tion of hydrochloric acid (specific gravity 1.115) at the boiling 
point of water for exactly 10 hours. In England the popular 
method is that proposed by Dyer, namely, to treat the soil with 
a I per cent, citric acid solution, this strength of solution being 
supposed at one time to represent the average acidity of root sap. 
^Maxwell, in Hawaii, and afterwards in Australia, claimed good 
results for the extraction of the soil with a i per cent, solution 
of aspartic acid, this acid being employed on the erroneous 
ground that the organic acids of the soil are amido acids, and 
that these are the effective agents in dissolving the soil minerals 
and rendering their constituents "available." The Kentucky 
Agricultural Experiment Station favors an X/5 nitric acid solu- 
tion,^ but does not recommend its use for soils of other localities, 
while in a contiguous state, the Tennessee Station favors the 
"official" method.- Many other methods have been proposed, 
but the foregoing are typical and sufficient to illustrate the pres- 
ent status of soil analysis. 

It is clear that tliese several methods must give dift'ering 
results. And it is not clear that any one of them is to be pre- 
ferred to the others for any reasons than analvtical convenieuce. 
There is no reason to expect that the proportion of solvent to 
soil required in these methods bears any relation whatever to 
the mechanism of absorption by plant roots. And the attempts 

' Soils, by A. M. Peter and S. D. Averitt, Bull. Xo. 126, p. 60, (1906). 
'The soils of Tennessee, by Charles A. Mooers. Bull. Xo. 78, p. 49, 
(1906). 



SOIL ANAIvYSIS AND INVESTIGATION II 

to simulate the properties of plant sap in some of these solvents 
are obviously illogical, for the plant sap does not come in con- 
tact with the soil grains, except through an accidental destruc- 
tion of the plant. 

Naturally, comparisons were attempted between the amounts 
of the mineral constituents extracted from a soil by these vari- 
ous solvents and the amounts taken up by crops growing on the 
soil. It was found, however, that the amount of any given 
mineral constituent extracted from the soil by a solvent is not, 
generally, the same as that taken up by the plant. Moreover, 
the ratio of one constituent to another in the extract bears no 
definite relation to the ratio of these constituents in the plant. 
Nevertheless many efforts were made to establish "factors." 
For instance, the percentage of potash extracted from the soil of 
a field by hydrochloric acid is some multiple of the percentage 
removed by a wheat crop ; it was sought to determine this multi- 
ple, assuming it to be a definite ratio and a natural constant, and 
it was designated as the potash factor. But there is a different 
factor for phosphorus, another for calcium, and still others for 
each and every constituent. The factors found for a soil from 
one area generally do not hold for a soil from another area. 
Again, different factors obviously must be used for diff'erent 
crops. And, finally, the whole scheme becomes hopeless when it 
is realized that the same crop will yield widel)^ varying ash 
analyses, depending upon the cultural methods employed, the 
judicious selection of seed, the amount and distribution of rain- 
fall and sunlight, and possibly other agencies, all of which affect 
the growth and absorptive functions of the plant to as great an 
extent as does the particular soil upon which it may be growing. 

Moreover, from the purely analytical point of view the situa- 
tion is no better. For instance, the addition of potassium in the 
amounts usually employed in ordinary fertilizer practice general- 
ly does produce a noticeable effect on the yield of crop. The 
average application of potash (KoO) is certainly less than 50 
lbs. to the acre. It is customary to consider the surface foot 
of soil as the region aft'ected bv the fertilizer, and an acre foot 



12 



THE SOIL SOLUTION 



in good moisture condition weighs about 4,000,000 lbs. To be 
conservative, let it be assumed that 60 lbs. of potash have been 
added to 3,000,000 lbs. of soil. The official method of the 
Association of Official Agricultural Chemists calls for the de- 
termination of the potash in 2 grams of soil, which on the basis 
of the present assumption calls for the estimation of an added 
amount of 0.00004 gi'am of potash or 0.002 per cent. Taking 
as an example the report of the Association of Official Agricul- 
tural Chemists for 1895^ there are given the following results 
obtained independently by a number of analysts, on soils which 
had presumably been sampled by the referee with all possible 
care : 

Potash Calculated As Per Cent, of the Fine Dried Earth. 



Analyst 


I 


3 


3 


4 


Per cent. 


Var. 


Per cent. 


Var. 


Per cent. 


Var. 


Per cent. 


Var. 


A 

B 

c 

D 

E 

F 

G 

Mean . • . 


0.359 
0.345 
0.354 
0.260 

0.373 
0.210 
0.304 
0.315 


0.044 

0.030 

0.039 

-0.055 

0.058 

—0.105 

—O.OII 


0.154 

O.II2 

' 0.235 

0.179 
0.130 
0.125 
0.156 


— 0.002 

— 0.044 

0.079 

0.023 
— 0.026 
—0.031 


0.380 
0.396 

0.365 
0.220 
0.286 
0.329 


0.051 
0.067 

0.036 
—0.109 
—0.043 


0.104 
0.225 

0.175 
0.109 
0.158 
0.154 


—0.050 
0.071 

0.021 

-0.045 

0.004 



Not only do the individual determinations show dififerences 
far in excess of 0.002 per cent., but the differences between each 
individual reading and the mean is greater than 0.002 per cent., 
so that it is evident from these results that the analytical pro- 
cedure fails to recognize appreciable amounts of the so-called 
available plant foods. Consequently the "acid digestion" of a 
soil fails of the purpose for which it was designed, and it is one 
of the mysteries of chemical history that so much time and energy 
have been devoted to such a hopeless quest. 

This state of affairs is the more surprising when the lim- 

* Proceedings of the Twelfth Annual Convention of the Association 
of Official Agricultural Chemists, Bull. Xo. 47, Division of Chemistry, 
U. S. Dept. Agriculture, p. 36, (1896). 



SOIIv ANALYSIS AND INVESTIGATION .13 

itations of the analytical procedure are considered. The data 
tabulated above indicate that the analyses were made with an 
exactness that justifies a statement to three decimal places, that 
is, to three significant figures ; and in fact, as was shown, such 
is necessary if the figures are to have any significance regarding 
fertilizer applications. It is obvious that the analysis of a finely 
pulverized definite mineral or rock is less subject to error than 
a sample of soil sifted through a 2 mm. mesh. Yet the U. S. 
Geological Survey commonly reports its analytical data to only 
hundredths of a per cent., that is, to two decimal places. What 
variation may be expected in duplicate determinations by the 
same analysts it is difficult to say, for such duplicates are not 
commonly published.^ In spite of the widespread view that the 
chemical analysis of a soil is a statement of great accuracy, it 
is improbable that as usually determined the potash content is 
correct to three or even two significant figures ; it is also doubt- 
ful if the phosphoric acid content is correct to even one signifi- 
cant figure, if the total amount is below o.i per cent, of the soil. 
That these determinations have a higher accuracy than here 
stated is not shown by an inspection of the literature including 
the fairly numerous results reported in the annual Proceedings 
of the Association of Official Agricultural Chemists. 

It was early felt by some investigators that soil analyses were 
unsatisfactory for studying the relation of the soil to the food 
requirements of a crop, and a second method was devised, name- 
ly, the growing of a crop, and determining the amount of 
mineral constituents removed from the soil by analyzing the ash 
of the crop. From the point of view of practical soil manage- 
ment this procedure involves the serious difficulty of being first 
obliged to get the crop before determining what must be done to 
best get it. It apparently has the scientific advantage of direct- 

^ See : On the interpretation of mineral analyses, by S. L. Penfield, 
Amer. Jour. Sci., (4), 10, 33, (1900) ; The analysis of silicate and car- 
bonate rocks, by W. F. Hillebrand, Bull. Xo. 305, U. S. Geol. Surv., 1907 ; 
Manual of the chemical analysis of rocks, by H. S. Washington, 1904, 
p. 24; Ueber Genauigkeit von Gesteinanalysen, von M. Dittrich, Neues 
Jahrbuch fiir Mineralogie und Palaeontologie, 2^ 69, (1903)- 



14 the; soil solution 

ness in determining- the mineral needs of the plant from the 
plant itself. If these needs were constant, the advantage would 
be real, but as already mentioned, one and the same plant may 
have a very different ash content as the result of different cul- 
tural methods, dift'erent climatic , and seasonal factors, as well 
as different soils. Generally, a poor crop has a higher per- 
centage of ash content than a good crop, and sometimes the 
poor crop may remove from the soil more in .absolute amounts of 
some one or other of the ash constituents than does the good 
crop. The ratio of the ash constituents is by no means constant 
for any one crop, and of course varies with different crops. ^ 
Finally, it is now known that the amount of the several mineral 
nutrients which a soil must furnish to a crop in the earlier stages 
of growth is greater than the crop contents at maturity,- con- 
sequently an analysis of the ripe crop would not indicate the 
plant's drain upon the soil at all growing periods. So that, 
while ash analyses have taught some important things concern- 
ing plant growth, they have of necessity failed as guides or 
criteria of the crop-producing power of a soil, its fertilizer re- 
quirements, or its content of "available" plant-food. 

A third method of soil investigation, also essentially analytical 
in character, is the plot or pot test. The dift'erence between 
a plot or pot experiment is mainly one of size, although it is 
claimed, and with a certain amount of justice, that the plot 
experiment more nearly approximates actual practice, and 
should be given a somewhat different consideration than the 
more readily controlled pot experiment. Here again it has to 
be considered that seasonal factors and factors other than the 
soil play a relatively large part in the production of the crop, so 
that conclusions regarding the productivity of a soil can not be 

' For a brief but comprehensive discussion of ash analyses see, The 
ash constituents of plants, etc., by B. Tollens, Expt. Sta. Rec, 13, 207- 
220, 305-317, (1901-02). 

" Uber die Nahrstoffaufnahmc dcr Ptlanzcn in verschiedcnen Zeiten 
ihres Wachstums, von Wilfarth, Rumer und Wimnier. Landw. Vers. 
Sta., 63^ 1-70, (1905) ; Plant food removed from growing plants by rain 
or dew, by J. A. Le Clerc and J. F. Breazcale, Year Book, U. S. Dept. 
Agriculture, 1908, p. 389-402. 



soil. ANALYSIS AND INVESTIGATION I5 

drawn from one season's crop. Also, nowadays it is recognized 
generally that continuous growing of one crop is an incorrect 
practice, and a rotation should be followed and repeated several 
times before conclusions regarding the productivity of the soil 
are justitied. If, however, the rotation has been well managed, 
the cultivation, fertilizing and soil management generally been 
well done for sixteen, twenty or more years, the soil has material- 
ly changed, and there can be no assurance that the treatment 
then best for it, is that which was best at the beginning of the 
experiment. Therefore the method throws no certain light on- 
the productive power of the soil, or the availability of its 
mineral plant-food constituents. Although much has been 
learned from plot experiments, and especially from the better 
controlled pot experiments, they are inadequate to meet the 
fundamental problem of the relation of the chemical character- 
istics of the soil to its crop-producing powers. 



Chapter IV. 

THE PLANT-FOOD THEORY OF FERTILIZERS. 

The guiding principle in soil investigations for about three- 
quarters of a century and until the past few years has been the 
assumption that the principal function of the soil is to furnish 
mineral nutrients to the plant, and that, to supply a lack in the 
soil, fertilizers are added because of the mineral plant nutrients 
they contain. This theory has apparently much to support it ; 
actually, however, the evidence usually cited accords better with 
a more comprehensive generalization which will be formulated in 
a later chapter. It is attractively simple. It will be shown 
later, however, that this very simplicity is an argument against 
its validity. 

Those substances which experience has shown to be useful 
soil amendments usually contain one or more of the constituents 
necessary to plant metabolism, commonly phosphorus, potassium, 
nitrogen or calcium. Fertilizers do not always produce in- 
creased yields of crops, but it has been usual to consider bad 
results as due to other more or less extraneous causes. More- 
over, as will appear later, crop yield is as strongly affected by 
some substances containing no mineral plant nutrient as by 
ordinary fertilizers. Again, the plant-food theory has been 
apparently confirmed by the popular misconception that crop 
yields are decreasing. Government statistics, however, indicate 
very positively that crop yields are increasing in Europe as well 
as in America, more in areas where the acreage is stationary 
than in areas where the acreage is increasing, and in areas where 
fertilizers are not used as well as in areas where they are used. 
Analyses of European soils which have been cropped for cen- 
turies show no characteristic differences from the newer soils of 
the United States.^ It is true that, from bad management or 
other causes, individual fields where crop production has fallen 

' A study of crop yields and soil composition in relation to soil 
productivity, by Milton Whitney, Bull. No. 57, Bureau of Soils, U. S. 
Dept. Agriculture, 1909. 



THE PI.ANT-FOOD THEORY OE FERTILIZERS 1/ 

off are not uncommon. But that such a condition is general 
or that it can be associated generally with a decreased content 
in the soil of any particular mineral substance or substances, is 
a conclusion not sustained by the available data. 

The plant-food theory of fertilizers must now be regarded as 
entirely insufficient. Granting that it has been useful -in the 
past and has occasioned much valuable work, it seems to have 
reached the point which another simple and temporarily useful 
theory, the phlogiston theory of combustion, reached s'nortly 
before the plant-food theory of fertilizers was evolved. Just as 
the phlogiston theory passed away when the elementary nature 
of oxygen was established and Lavoisier taught the scientific 
world to use the balance, so the plant-food theory of fertilizers 
must pass with increasing knowledge of the relation of soil to 
plant and the application of modern methods of research to the 
problem. 



Chapter V. 



THE DYNAMIC NATURE OF SOIL PHENOMENA. 

In soil investigations, until recently, the assumption has been 
made, more or less explicitly, that any given soil mass, as for 
instance a field, remains fixed or in place indefinitely. It has 
been admitted, of course, that some physical, chemical and 
biological processes might be taking place in the soil, but these 
have been regarded as relatively unimportant in their etTects 
upon the soil mass /;/ toio. It has been assumed that the only 
important change taking place in the soil is a loss of mineral 
plant nutrients, partly by leaching, partly by removal in the 
garnered crops. In other words, the soil has been regarded as 
a static system. This is a fundamental error. In studying the 
soil as a medium for crop production, we must consider the 
plant itself, or at least that part of the plant which enters the 
soil, namely, the root ; the solid particles of the soil ; the soil 
water, or the aqueous solution from w^hich the plant draws all 
the materials for its sustenance, excepting the carbon dioxide 
absorbed by its aerial portions ; the soil atmosphere ; the biologi 
cal processes taking place. The one common characteristic of 
all these things is that they are continually in a state of change ; 
therefore tne soil problem is essentially dynamic. 

The root of a growing plant is alwa_\s moving.^ The amount 
of motion mav be small or large, depending upon the surround- 

' In order to penetrate the soil, a living root must 1)e capable of 
exerting large pressures, and indeed, the magnitude of these pressures 
has been determined for some cases. See, for citations of the literature 
Pfefifer, Plant Physiology, translated by Ewart, 1903, Vol. 2, p. 124 <-/ sc(i 
But it can not be doubted that, in general, root movement is nuicl 
facilitated and perhaps directed by movements among the soil particles. 
As the absorbing tip of the root removes film water from the adjacent 
soil grains, there is a necessary rearrangement of these grains with a 
shrinking away from the tip, which then moves forward by taking ad- 
vantage of the movements among the soil grains. 



THE DYNAMIC NATURE OF SOIL PHENOMENA I9 

ing conditions or attendant circumstances, but cessation of mo- 
tion means the death of the root. This becomes evident from a 
consideration of the mechanism of root growth. The living 
root absorbs and excretes water and dissolved substances through 
a restricted area just back of the root tip or the tips of the root 
hairs. While absorption is taking place, however, there is a 
deposition of denser material over the absorbing area, or "root 
corking."' But coincident with the corking process, the tip is 
pushed forward between the soil grains into the nutrient medium, 
new cells are formed and a new absorbing surface continually 
brought into functional activity. A failure of the plant root 
to move forward in this way would mean a reabsorption of root 
effluvia with harmful consequences to the plant, or a corking over 
of the root without further formation of absorbing surface and 
with consequent cessation of its functioning. This would mean the 
inevitable death of the root, and, if general, of the whole plant. 
It is clear, therefore, that root penetration and absorption of 
plant nutrients are essentially dynamic. 

The solid components of the soil are always in motion. 
Every soil, no matter how flat the area or how well protected 
by vegetal covering, suffers some translocation of soil material 
through rains, as is evidenced by suspended material in the run- 
off waters. On hillsides this is shown by the soil accumulating 
on the "up" sides of fences, especially stone fences. In the 
aggregate this movement is probably quite large everywhere. 
It is manifestly so in the watersheds of many of the world's im- 
portant rivers as shown by their muddy waters and the forma- 
tion of deltas, sometimes of great area and agricultural im- 
portance. 

With the saturation or approach to saturation of the sur- 
face soil the particles are more easily moved among themselves 
by an extraneous force. It is very rarely that the surface of a 
field is a dead level. Consequently when the soil is wetted, the 
gravitational force on the individual soil grains produces a more 
or less pronounced "creeping" effect down hill. On decided 



20 the: soil solution 

slopes this soil creep is believed to be of great importance in 
connection with soil erosion.^ 

As important as is the translocation of material by water, 
quite as important probably is that produced by the winds. 
These are blowing all the time, uphill as well as down, and 
their range of action is thus far wider than is that of rain and 
flood. The effectiveness of the wind as a translocating agency 
is seldom realized or even suspected by the layman, although 
it is commonly known that the air always contains some dust, 
and dust storms are familiar phenomena. That soil material 
can be carried long distances is certain, however, as for instance 
the sirocco dust, often carried from the Sahara over Europe. - 
Dust carried high into the air by volcanic eruptions sometimes 
travels enormous distances, as in the case of the eruption of 
Krakatoa, when such material is reported to have traveled 
thousands of miles, and volcanic debris from the eruptions at 
Soufriere fell upon ships several hundred miles distant. Arctic 
explorers have reported the finding of wind-borne soil materials 
over the polar ice, and mountaineers have observed similar 

' Soil erosion is undoubtedly one of the greatest economic problems 
of the time, and yet there is scarcely any subject about which there are 
current so many popular misconceptions. In the rivers and to those who 
use the rivers the water-borne soil material is an unmitigated nuisance, 
save possibly to a few cultivators of low-lying lands who for one reason 
or another, may flood their fields for the sake of the silt deposited. 
To the upland farmer, however, erosion is not only a necessity of natural 
conditions which can not be avoided entirely, but under proper control 
it may be even a blessing. The scalded and gullied hillsides, a trial and 
unnecessary disgrace to the owner, are probably not the main sources 
of the material which finds its way to the river. On the contrary, what 
are regarded usually as well-tilled fields supply the greater part of the 
suspended material in the rivers. The problem of erosion on the farm 
is not merely to check gullying and scalding, and deepening of stream 
heads, but to so adjust both cropping system and cultural methods as to 
secure a reasonable translocation of surface soil material with a mini- 
mum contamination of the neighborhood streams. See, IMan and the 
earth, by Nathaniel Southgate Shaler, 1905. 

' For a comprehensive discussion of wind as a translocating agent, 
see: The movement of soil material by the wind, by E. E. Free, Bureau 
of Soils, Bull. No. 68, U. S. Dept. Agriculture. 



the; dynamic nature of soii. phenomena 21 

deposits on snow-capped peaks. Soil material on roofs and 
similar inaccessible places has been observed many times, and 
testifies to the continual activity of the wind. The burial of 
objects even of considerable size by wind-borne soil gives like 
testimony. 

Measurements of the amount of action of wind in trans- 
locating- soil material are rare and probably have a qualitative 
value only. But Udden^ in what appears to be a conservative 
calculation, finds ''the capacity of the atmosphere [over the 
Mississippi Valley] to transport dust is looo times as great as 
that of the [Mississippi] River." The wind seldom is carrying 
anything like so great a load as it is capable of carrying. That 
is, the wind in its attack upon the land surface does not ordinari- 
ly obtain so large an amount of material capable of being wind- 
borne as it is possible for the wind to carry when suitable ma- 
terial is artificially provided. It should be remembered that, 
speaking generally, the velocity of the wind is lower just at the 
surface of the ground than at heights above, and it is necessary 
to get the soil material above the surface before the wind can 
exercise its full efficiency as a carrying agent. 

Moreover, wind-borne material is constantly being deposited 
as w^ell as being removed from the land surface. It is evident, 
however, that this movement of soil material by winds is very 
great, and there is no reason to believe that it is of any less 
importance in other areas than in the Mississippi Valley. It is 
also evident that the individual grains in any surface soil of any 
particular field or area are continually and more or less rapidly 
changing, and the farmer is not deahng to-day with just the 
same soil complex he faced a few years back, or will face a few 
years hence. 

But besides the movements of the solid components of the 
soil by translocating agencies, other movements are constantly 
taking place. Whenever a moderately dry soil becomes wetted, 
it "swells up" until a certain critical amount of moisture is 
present above which there is a shrinking. But as a wet soil 
^ Erosion, transportation and sedimentation performed by the atmos- 
phere, by J. A. Udden, Jour. Geo!., 2, 318-331 (1894). 



22 THE soil, SOLUTION 

dries out again below the critical amount, there is again a shrink- 
ing. As it is always either raining or not raining, soils are al- 
ways either getting wetted or are drying. Consequently the 
individual grains are continually moving about among them- 
selves. A heavy object, such as stone, when left on the ground 
gradually sinks into it.^ Earthworms, burrowing animals and 
insects are continually at work in most arable soils. The action 
of frost in "heaving" a soil is familiar to everyone. Not so well 
known, however, is the fact that the apparently superficial cracks 
which occur to a greater or less extent in every soil, under 
drought conditions, are in reality quite deep, extending well into 
the subsoil. By the edges breaking off, and by wind- and water- 
borne material being carried in, considerable surface soil is thus 
brought into the subsoil. Through these various agencies, 
therefore, the solid components of the soil are continually sub- 
ject to much mixing; subsoil is becoming surface soil, and to 
some extent vice versa. An important result of these various 
processes is the bringing into the surface soil of degradation and 
decomposition products from underlying rocks. Tlie processes 
involved are essentially dynamic. - 

The soil solution is also a dynamic problem. AMien the rain 
falls on the soil, a part, the "run-oft"," flows over the surface and 
finds its way into the regional drainage ; a part immediately 
evaporates into the air, and is designated as the "fly-off ;" a 
third part, the "cut-off," enters the soil.^ The cut-oft' water 
penetrates the soil by way of the larger openings and interstices, 

^ On the small vertical movements of a stone laid on the surface of 
the ground, by Horace Darwin, Proceedings of the Royal Society of 
London, 68, 253-261, (1901). On the other hand, geological literature 
would probably furnish numerous references to the heaving out of 
boulders, probably as the result of successive freezings and thawings of 
the soil. The shape of the stone as well as the specific nature of the 
movements of the soil particles evidently has an important influence in 
determining whether the stone sinks into the soil or vice z-crsa. 

■ It is clear that as the soil is continually changing through physical 
agencies, the chemical analysis of it can not be expected to furnish 
evidence as to the mineral constituents removed by crops or by leaching. 

^ This terminology has been suggested by Dr. W J McGee. 



THE DYNAMIC NATURE OF SOIL PHENOMENA 23 

and mainly under the influence of gravity. For convenience this 
downward-moving water is designated as "gravitational" water. 
It moves through the soil with comparative rapidity and a por- 
tion reappears elsewhere as seepage water, springs, etc. But 
with the return of fair-weather conditions at the surface, there 
is increased evaporation and augmentation of the fly-off, and 
there is developed a drag or "capillary pull" on the water belov/. 
A large portion of the cut-off thus returns to the surface, main- 
ly through films over the surface of the soil grains and in the 
finest interstices.^ 

The soil atmosphere is continually in motion, following with 
more or less decided lag the barometric changes in the atmos- 
phere above the soil. Moreover, the chemical and physical pro- 
cesses continually taking place in the soil involve the absorption 
or the formation of free carbonic acid, and it seems probable that 
all rain water penetrating the soil gives up some oxygen to the 
soil atmosphere. The bacteria and lower life forms are nec- 
essarily undergoing changes continually. In fact all compo- 
nents of the soil are continually undergoing, or are involved 
in, changes of. one kind or another. 

It is certain that investigation of the various motions and 
changes taking place in the soil is quite as important as investi- 
gation of the soil components, and that no clear idea of the 
chemistry of the soil can be obtained without it. The develop- 
ment of a rational practice of soil control is possible only when 
the soil is regarded from a dynamic viewpoint. 

^ Leather, however, thinks the water returns from only a limited 
depth, some 5-7 feet ; see, The loss of water from soil during dry weather, 
by J. Walter Leather, Memoirs of the Department of Agriculture, 
Agricultural Research Institute, Pusa, India, CTiemical series, i, 79-116, 
(1908). Dr. George N. Coffey has called the author's attention to some 
observations in Western Kansas, where a prolonged drought had dried 
the soil to a considerable depth. A fairly heavy rain wetted the soil 
to less than two feet from the surface, and practically all of this mois- 
ture had returned to the surface and evaporated within a few days. 
Such special cases as these, however interesting in themselves, are even 
less so than the normal cases in humid areas, where a part of the water 
passes through the soil as seepage, the larger portion returning to the 
surface, sometimes through distances of many feet. 



Chapter VI. 



THE FILM WATER. 

\A'lien a relatively small quantity of water is added to an 
absolutely dry soil or other powdered solid, there is some shrink- 
age in the apparent volume of the soil or powder. The water 
spreads over the surfaces of the solid particles in a film, and a 
rise in temperature shows that a noticeable energy change ac- 
companies the formation of the film.^ With further increments 
of water the apparent volume of the soil increases until a maxi- 
mum is reached. The water content at which this maximum 
volume of soil can be attained is a definite physical characteristic 
for any given soil. What is popularly known as the "optimum 
water content" corresponds to this critical content.^ It is the 
point at which further additions of water will not increase the 
thickness of the moisture film on the soil grains, but will give 
free water in the soil interstices. Just as the apparent volume 
of a given mass of soil varies with the water content, and reaches 
a maximum at a critical moisture content, so do all the physical 
properties vary and have either a maximum or minimum value 

See, in this connection, Energy changes accompanying absorption, 
by Harrison E. Patten, Trans. Am. Electrochem. Soc, u, 387-407, (1907) ; 
see also the recent valuable research, Les degagements de chaleur qui 
se produisent an contact de la terre seche et de I'eau, par A. jMuntz et 
H. Gaudechon, Ann. sci. agron. (3), 4» II, 393-443, (1909), where it is 
shown that probably a part of the heat is due to chemical combination 
between the water and the other soil components. To quote, "Ces di- 
verses observations nous conduisent a peuser, sans nous en donner 
toutefois la preuve absolute, que la fixation de I'eau sur les elements 
terreux tres fins et sur les materiaux organises, est tout au moins, en 
partie, attribuable a une combinaison chiniique qui se manifeste non 
seulement par un fort degagement de chaleur, mais aussi par la soustrac- 
tion de I'eau a des substances aux-quelles elle semble chitniquement 
liee." 

' The moisture content and physical condition of soils, by Frank 
K. Cameron and Francis E. Gallagher, Bull. No. 50, Bureau of Soils, 
U. S. Dept. of Agriculture, IQ08. See also Uber physikalische Bodenun- 
tersuchung, von H. Rodewald. Schriften Xaturwiss. Vereins Schleswig- 
Holstein, 14, 397-399, (1909)- 



THE FILM WATER 25 

at this same critical moisture content. Thus the apparent 
specific gravity of a soil reaches a minimum, the force required 
to insert a penetrating tool becomes a minimum, while the rate 
at which a soil warms up reaches a maximum,^ and the ease 
with which aeration takes place reaches a maximum. In fine, 
this critical water content is that at which the soil can be brought 
into the best possible physical condition for the growth of crops. 
The practical significance of the optimum water content is far 
greater than would be supposed from the attention given it 
hitherto by students of the soil. It is the content of soil water 
which the greenhouse man should strive to maintain, and which 
the irrigation farmer should seek to provide, instead of the over- 
wetting so common to the practice of both. In general farming 
it is that moisture content at which the farmer will attain the 
best results in plowing and cultivating, and attain these results 
most readily. 

With additions of water beyond the critical point, there is a 
presence of free water in the soil interstices accompanied by im- 
portant changes in the soil structure. With continued addi- 
tions, there is a more or less rapid decrease in the apparent 
volume; there is a tendency for the soil aggregates to break 
down and the "crumb structure" so greatly desired by agri- 
culturists is less and less readily obtained, and workings of the 
soil tends in some cases to produce that phenomenon known as 
"puddling." However desirable the property of puddling may 
be to the potter or the brick maker, to the farmer it is a bane 
to be avoided above all things. To overcome it requires his best 
skill, and it usually takes several years of patient efifort tO' re- 
store a puddled soil to good tilth. 

The force with which the film water is held against the soil 
grains has not been determined as yet with any degree of pre- 
cision, but it is certainly very great. If a soil be saturated, that 
is, if so much water be added that further additions will cause a 
flow of free water, and the soil be then submitted to some 
mechanical device for abstracting the water, the moisture content 

^ Heat transference in soils, by Harrison E. Patten, Bull. No. 59> 
Bureau of Soils, U. S. Dept. Agriculture, 1909. 
3 



26 THE SOIL SOLUTIOX 

of the soil can be readily diminished to the critical water content ; 
but to diminish it further by mechanical means is not easy. The 
tenacity with which film water is held by the soil grains has been 
shown in several ways. In one of these, for instance, a semi- 
permeable membrane was precipitated in the walls of a porous 
clay cell, which was then filled with sugar solution having- an 
osmotic pressure of about 35 atmospheres. When this cell was 
buried in a soil having a moisture content above the optimum, 
water flowed into the cell. On the contrary, when the cell was 
buried in another sample of the same soil having a moisture con- 
tent well below the optimum, there w^as a marked flow of water 
from the cell. It would appear, therefore, that the attraction 
between the soil grains and the film-forming water was certainly 
greater than the solution pressure of the sugar.^ Again, by 
whirling wetted soils in a rapidly revolving centrifuge,- fitted 
with a filtering device in the periphery, and developing a force 
equivalent on the average to 3,000 times the attraction of gravita- 
tion, the soils could not be reduced below the critical water con- 
tent. From the results of Lagergren,^ Young,* and Lord 
Rayleigh,^ it appears that the force holding a very thin moisture 
film on the soil grains would be of an order of magnitude from 
6,000 to 25,000 atmospheres. This force, however, must greatly 
decrease with thickening of the film, as is shown by the fact 
that at the critical moisture content a small further addition of 
water produces no marked heat manifestation, though making 
a noticeable difference in the physical properties of the soil. 

^ The chemistry of the soil as related to crop production, by Milton 
Whitney and Frank K. Cameron, Bull. No. 22, Bureau of Soils, U. S. 
Dept. Agriculture, 1903, p. 54. 

■ The moisture equivalent of soils, by Lyman J. Briggs and John W. 
McLane, Bull. No. 45, Bureau of Soils, U. S. Dcpt. Agriculture, 1907. 

' Uber die beim Benetzen fein verteilter Korper auftretende W'arme- 
tonung, von Lagergren, Bihang till K. sv. Vet.-Akad., Handl., 24» Afd. II, 
No. 5- (1898). 

''Hydrostatics and elementary hydrokinctics, George M. Minchin, 
p. 311, 189-3. 

° On the theory of surface forces, by Lord Rayleigh, Phil. Mag. (s), 
30, 285-298, 456-475, (1890). 



THE FILM WATER 27 

Therefore, while recognizing that our knowledge of this force 
still lacks a desirable precision, it is nevertheless clear that the 
force is very great. 

The function of the film water in maintaining the soil struc- 
ture is undoubtedly important. A soil in good tilth, or good 
condition for crop growth, shows a peculiar structural arrange- 
ment of the individual soil grains or soil particles, which it is 
very difficult to describe in precise terms, but which is readily 
recognized in practice. This condition is usually described as a 
"crumb structure," either because of its appearance or be- 
cause of the peculiar crumbly feeling which a soil in this con- 
dition gives when rubbed between the fingers. The individual 
grains of soil are gathered into groups or floccules. While other 
causes may be more or less operative in particular cases, it seems 
very probable that the film water is primarily the agency holding 
together the grains in these floccules. The obvious explanation 
is that the film is exerting a holding power because of its sur- 
face tension. It follows, therefore, that anything which afifects 
the surface tension of water should afifect the structure of the 
soil ; that is, the flocculation or granulation of the particles. But 
certain agents which produce respectively flocculation or de- 
flocculation, nevertheless modify the surface tension of the solu- 
tion in the same direction, and in not widely varying degree. 
Similar difficulties arise in attempting to correlate "crumbing" 
phenomena with the viscosity of the film water,^ and it must 
be admitted frankly that present views on this subject are very 
unsatisfactory, and that more careful investigation is urgently 
needed on this fundamental and important problem. Not only 
is the absence of a satisfactory theory embarrassing in consider- 
ing the problems of soil structure and a rational control, but the 
difficulties are no less in the ec|ually important problems of the 
movement of film moisture, and the distribution of moisture in 
a soil. 

^ Equally unsuccessful is the attempt to correlate flocculating agents 
with changes in the density of water. See. The condensation of water 
by electrolytes, by F. K. Cameron and W. O. Robinson, Jour. Phys. 
Chem., i4> i-ii, (1910). 



28 



THE SOIL SOLUTION 



The movement of moisture into a soil from an illimitable 
supply is a comparatively simple phenomenon, controlled by a 
rate law which may be expressed by the equation j" == k^ when 
y is the distance through which the movement has taken place ; 
/ is the time, and k and n are characteristic constants for the 
particular soil and solution.^ This expression may be more 
readily recognized as a rate formula when written dyjai =^ ^y"', 
where A and m are constants for the particular system. The 
first form of the equation promises to be the more useful. 
This formula also describes the rate of advance of a dissolved 
substance into the soil. 

Owing to irregularities in the soil column this equation is 
more readily studied with capillary tubes or with such absorbents 
as filter-paper or blotting paper. The following tables will, 
however, give an idea as to its validity for soils. 
AivLuviAi. Soil, Gila River.'' 



Time, ' min. 


Height,-' inches 


X- (h = 1.S6) 


2 


1-5 


1.05 


5 


2.4 


1.02 


lo 


3.6 


1.08 


15 


4-3 


1. 01 


30 


6.3 


1.05 


60 


9.2 


1.07 



Distilled Water in Penn. Loam ( i — 21° C). 



Time, ' 


Height, ^ 


k 


Time, ' 


Height, > 


k 


min. 


cm. 


{n = 2.25) 


min. 


cm. 


(n = 2.25) 


I 


■ I- 15 


1-37 


20 


390 


1.07 


2 


1-54 


1-33 


30 


467 


1.06 


3 


1.85 


1-33 


40 


5-39 


I. II 


4 


2.08 


1.30 


50 


5-9" 


1.09 


5 


2.28 


1.28 


60 


6.47 


1. 12 


7 


2.59 


1. 21 


75 


7.20 


I-I3 


10 


297 


1. 16 


90 


8.03 


1. 21 


15 


3-47 


1. 10 


105 


8.72 


1-25 



1 See Bull. No. 30, Bureau of Soils, U. S. Dept. Agriculture, p. 50 
et seq.; also, The flow of liquids through capillary spaces, by J. M. Bell 
and F. K. Cameron, Jour. Phys. Chem., 10, 659, (1906): See also, Wo. 
Ostwald, 2 Supplementheft Zeitschrift Kolloidchemie, 1908, 20. 

^ Computed from observations by Loughridge, Report Agr. Expt 
Sta., University California, 1893-94, p. 93. 



the; film water 



29 



Indigo Carmine in Penn. Loam Soil ( / = 21° C.)- 
Solution contained 2 grains dye per liter. 



Time, ' 


Height, y 


k for water 


Height colored 


k for dye 


mill. 


wet cm. 


(n = 2.25) 


cm. 


[n = 2.25) 


I 


1.28 


1-75 


0.64 


0.37 


2 


1.67 


1-59 


0.90 


0.39 


3 


2.05 


1.68 






4 


2.26 


1.56 






5 


2.49 


1.56 


1.02 


0.21 


7 


2.74 


1.38 






10 


3.20 


1.40 






15 


3-72 


1.29 






20 


4.28 


1.32 


1.92 


0.22 


30 


5.10 


I-3I 






40 


5-77 


1.29 


2.69 


0.23 


50 


6.41 


1.26 


3.20 


0.28 


60 


6.90 


1.29 






75 


7.46 


1.23 






90 


8.74 


1.46 


3-59 


0.20 


105 


9.00 


1-33 


• • 





It has also been shown repeatedly by experiment that the 
movement of moisture is relatively rapid when the moisture con- 
tent of the soil is above the optimum, but that the movement is 
exceedingly slow when the soil has a lower water content than 
the optimum ; that is, the point at which the water is entirely in 
the form of film water. For instance, if a moderately wet sam- 
ple of soil be broug-ht into intimate contact with an air-dry sample 
of the same soil, there will, at first, be a relatively rapid move- 
ment of the moisture, but as soon as the wetted portion has been 
brought to the "optimum" condition, no further movement can 
be detected, although the experiment has been tried of leaving 
such samples together for months and with a difference of water 
content amounting, in the case of clay soils, to 15 or 20 per 
cent. Since the drought limit, or the soil moisture content at 
which plants wilt, is, for most soils, considerably below the 
optimum water content, the movement of film water is obvious- 
ly a problem of the first importance from a practical point of 
view as well as of the highest theoretical interest. 

The movement of water vapor, or its distillation from place 
to place in the soil, is another problem often confused with the 
above. Its importance is not yet clear, although according to 



30 THE SOIL SOLUTION 

some investigators^ it would appear that the addition of soUible 
fertilizer salts by causing a lowering of the vapor pressure of the 
water induces a distillation to that region from other regions of 
the soil as well as from the atmosphere above. This brings up 
the problem of the diffusion of water and other vapors throvigh 
the soil. It has been shown that the soil "plug" retards the 
rate at which diffusion takes place but induces no other effect 
in the ordinary phenomenon of free diffusion. This fact is 
obviously of the first importance in the theory of mulches, but 
requires no further consideration here.- 

^ Sur la diffusion des engrais salins dans le terre, par ]\Iuntz et 
Gaudechon, Comptes rendus, 148, 253-258, (1909). 

' See, Contribution to our knowledge of the aeration of soils, and 
Studies of the movement of soil moisture, by Edgar Buckingham, Bulls. 
Nos. 25, 1904, and 33, 1907, Bureau of Soils, U. S. Dept. of Agriculture 



Chapter VII. 

THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION.^ 

The mineral constituents of the soil are products of the dis- 
integration, degradation and decomposition of rocks. The de- 
composition products are mainly silica in the form of quartz, 
ferruginous material consisting of more or less hydrated ferric 
oxide and alumina, and hydrated aluminum silicate. The 
ferruginous material, being deposited or formed in the soil in a 
very finely divided condition, frequently coats the soil frag- 
ments to such an extent as completely to mask their true char- 
acter. But if a soil be thoroughly shaken with water, and 
especially in the presence of some deflocculating agent such as a 
slight excess of ammonia, as in the ordinary preparation of a 
soil sample for mechanical analysis- the coating material is 
generally removed quite readily, and the mineral particles appear 
as fragments and splinters of the ordinary rock-forming miner- 
als. Sometimes these fragments are more or less worn and 
rounded at the edges, showing mechanical abrasion or solvent 
action ; sometimes they show evidences of partial alteration and 
decomposition ; but surfaces of the unaltered mineral individuals 
always are found. These unaltered minerals occur as fragments 
of all sizes, and are to be found in the sands, silts, and presum- 
ably in the clays. As might be anticipated, the minerals other 
than quartz generally show a tendency to segregate in the finer 
mechanical separations of the soil. The presence of these un- 
altered mineral fragments in the clays has so far defied direct 
experimental proof because of the limitations of the microscope, 
but from chemical reasoning and a priori considerations there 

' For a more detailed discussion and citations of the literature, see 
The mineral constituents of the soil solution, by Frank K. Cameron 
and James M. Bell, Bull. Xo. 30, Bureau of Soils, U. S. Dept. Agricul- 
ture, 1905. 

" Centrifugal methods of mechanical soil analysis, by L. J. Briggs, 
F. O. :\Iartin and J. R. Pearce. Bull. Xo. 24. Bureau of Soils, U. S. 
Dept. Agriculture, 1904. 



32 THE SOIL SOLUTION 

can be but little doubt that they exist in the clays as in the 
coarser separations.^ 

The minerals to be anticipated in the soil are those commonly 
occurring in the rocks ; but as a result of the action of mixing 
and transporting agencies, a soil normally contains minerals from 
rocks other than those from which it is primarily derived. 

It would hardly be fair to regard a beach sand, for instance, as 
a normal soil. Yet it is surprising how many minerals other 
than quartz can usually be found even in a beach sand. 
Opinions may differ as to just what are the common rock-form- 
ing minerals, and perhaps no two mineralogists or petrographers 
would give identical lists, but there are a number of minerals 
w^hich would appear undoubtedly in every list, and these would 
be found generally in any soil. Again, it might happen that in 
any given sample of soil, no pyroxene, for instance, could be 
found ; but experience shows that it would never happen in such 
a case that no amphibole, chlorite, serpentine, or other ferro- 
magnesian silicates would be present. However distinct these 
minerals cited may be from each other morphologically or 
optically, they are much the same in their chemical character- 
istics, their solubilities and their reactions with water and such 
dilute solutions as exist in the soil. Hence from the point of 
view of the soil chemist they may be considered for all practical 
purposes varieties of one and the same mineral species. Con- 
sequently an important result of researches on the minerals of 
the soil is the generalization that soils are far more heterogeneous 
than are rocks, and that practically every soil contains all the 
coiiiuwn rock-forniiuQ; niincrals.- 

It is not difficult to account for the heterogeneity of the miner- 
al content of the soil. Many of our rocks are reconsolidated 

' See, The mineral composition of soil particles, by G. H. Failyer, 
J. G. Smith and 11. R. Wade, Bull. No. 54. Bureau of Soils, U. S. Dept. 
Agriculture, igoQ. Recent improvements in microscope methods make it 
possil)le to identify without serious trouble the mineral content of silts 
with a diameter as low as 0.005 mm., and many even of the clay parti- 
cles have recently been determined with satisfactory'^ accuracy. 

2 See Bull. No. 30, Bureau of Soils, U. S. Dept. Agriculture, 1905, 
p. 9- 



the; minerai, constituents of the soil solution 33 

soils, and the alternating formation of rock and soil from the 
same materials is probably an agency, in some part at least, in 
the mixing of soil material. The action of water in carrying 
ofif and transporting surface material and in gullying and erod- 
ing sloping surfaces is probably a large factor. But this agency, 
like the first, is rather restricted and localized. Just as important 
as a mixing agency is the wind. This, unlike water, works up- 
hill as well as down, and is more or less in action at all times, 
continually transporting soil material from place to place. Wind- 
borne dust on roofs of dwellings, on rocky mountain tops and 
similar places, where it could have been brought by no other 
agency than the wind, is sometimes found supporting vegetation. 
Many chemical and mineralogical analyses of wind-borne dust 
obtained from various locations show it to have generally the 
same essential characteristics as ordinary soils. 

Aside from the quartz and ferruginous materials mentioned 
above, the major part of the soil minerals are silicates, ferro- 
silicates, alumino-silicates or ferro-alumino-silicates, of the com- 
mon bases, sodium, potassium, calcium, magnesium, and ferrous 
iron. Other bases, such as lithium, barium, or the heavy metals 
may occasionally be present in appreciable amounts as may 
other types of silicates, or other mineral salts, but these may be 
regarded as more or less incidental and rarely affecting in any 
essential way the general character of the soil mass. These 
silicates or silico minerals are all somewhat soluble in water, 
and being salts of weak acids with strong bases, are greatly 
hydrolyzed. A convenient illustration is afforded by the well- 
known rock and soil mineral, orthoclase. Assuming its type 
formula, the reaction with water may be represented, 

K.AlSiA + HOH ZZ H.AlSisO, + KOH. 
Under ordinary soil conditions, with a relatively large propor- 
tion of carbon dioxide in the soil atmosphere, the potash formed 
would be more or less completely transformed to the bicarbonate, 

KOH + CO, + H,0 !ri KHCO3 + H,0. 
Confirmation of this view is afforded by the natural associa- 
tions and known alteration products of orthoclase. 



34 THE SOIL SOLUTION 

The acid of the formula H.AlSisOs is not known and is 
probably entirely instable under ordinary conditions, and breaks 
down with the separation of silica, to form the minerals pyro- 
phyllite. kaolinite or kaolin, and diaspore according to the follow- 
ing equations : 

H.AlSi.Os — SiO, = H.AlSi,0„ ( Pyrophyllite) 
H.AlSigOs — 2Si6, = H.AlSiO, (KaoHnite) 
H.AlSi308 — aSiOo = H.AIO, (Diaspore). 

All three of these minerals and their corresponding salts have 
been found in nature as alteration products of orthoclase. It 
is probable that, under sod conditions, the principal metamorphic 
product of feldspar is kaolin (or kaolinite when it is crystalline), 
hydrated aluminum oxide being of much less importance^ and 
pyrophyllite of doubtful occurrence. A still more interesting 
case, perhaps, because of the well recognized tendency of mag- 
nesium salts to form basic compounds, is the alteration of 
pyroxene, amphibole and olivine with the formation of a chlorite 
or serpentine, common associations in nature, which may be 
represented 

MgSiOg + HOH tl MgSi03.:'^Mg(0H), + SiO,. 

It is tacitlv assumed in the foregoing statements that the re- 
action between a silicate mineral and water is a reversible re- 
action. This is not definitely known to be the case, for the for- 
mation of the ordinary silicate rock-forming minerals in the wet 
way at ordinary temperatures has as yet been realized in only a 
few cases. The assumption has, however, some experimental 
support. ^Minerals have been often made in the wet way at 
somewhat elevated temperatures, especially interesting cases in 
this connection being the formation of orthoclase by Friedel and 
Sarasin- at slightly elevated temperatures, and the formation of 

^ See Ueber die Bildung von Bauxit und verwandte Mineralien, von 
A. Liebrich, Zeit. prakt. Geol., 1897, 212-214. 

' Sur la reproduction par voie aqueuse du feldspath orthose, par 
Friedel et Sarasin, Comptes rendus, 92, 1374, (1881). 



the; mineral constituents of the soie solution 35 

zeolites by GpnnarcF and by Doroshevskii and Bardt," and the for- 
mation of apatite by Weinscheni<.^ Feldspars and zeolites are com- 
mon natural associations, it being- generally conceded that zeolites 
are alteration products of the feldspars through the action of water ; 
but Van Hise* has pointed out that under conditions of weathering 
such as would obtain in the soil, the tendency is for the zeolite3 
to alter to feldspars. Wohler's classical experiment of re- 
crystallizing apophyllite from hot water^ is significant, for only 
the products of hydrolysis should be obtained if there is an ir- 
reversible reaction between the mineral and water. Lemberg 
found that leucite (KAlSi^Og) when treated with an aqueous 
solution containing lo per cent, or more of sodium chloride, was 
partially transformed to analcite (NaAlSioOg-w-HoO), potassium 
chloride being formed at the same time. The reverse reaction 
was also realized, that is, the partial conversion of analcite to 
leucite by treatment with a solution of potassium chloride, and 
similar transformations were carried out with the feldspars.*' 
Lemberg's experiments are of especial value as they were carried 
out at ordinary as well as at high temperatures. It appears pro- 
bable, therefore, that the hydrolysis of a silicate of the alkalis or 
alkaline earths is a reversible reaction. It should be noted, how- 
ever, that Kahlenberg and Lincoln' have shown that probably, 
in very dilute solutions of alkali silicates, the hydrolysis is 

^ Xote sur une observation de Fournet, concernant la production 
des zeolites a froid, par F. Gonnard. Bull. Soc. min. France, 5, 267- 
269, (1882) ; Jahrb. Mm., 1884, I. Ref. 28. 

" Metathetical reactions with artificial zeolites, by A. Doroshevskii 
and A. Bardt, Jour. Russ. Phys. Chem. Soc, 42, 435-42 (1910). Chem. 
Zentr., 1910, II, 68. 

' Beitrage zur Mineralsynthesis, von E. Weinschenk, Zeit. Kryst., 17, 
489-504, (1890). 

* U. S. Geol. Surv. Monograph, 47» A treatise on metamorphism, by 
Charles R. Van Hise, 1904, p. 333. 

'Jahresb. Fortschr. Chemie Liebig and Kopp, 1847-48, 1262; note. 

° Ueber Silicatumvifandlungen, von J. Lemberg, Zeit. deutsch. geol. 
Ges., 28, 519-621, (1876) ; Inaug. diss. Dorpat, 1877; Bied. Centbl., 8, 

567-577, (1879). 

^ Solutions of silicates of the alkalis, by L. Kahlenberg and A. T. 
Lincoln, Jour. Phys. Chem., 2, 77-90, (if 



36 THE SOIL, SOLUTION 

practically coinplete and the silica is nearly all present as colloidal 
silica and not as silicic acid. Nevertheless at higher concentra- 
tions silicates are formed, and there is abundant evidence in 
nature that the alumino- or ferro-silicates arc reacting with bases 
to form salts, for example such as the micas. ^ If the hydrolysis 
were quite complete, it would appear to follow that the reaction 
between water and the silicate is irreversible. In that case it is 
difficult to see how any silicate mineral could persist in the soil 
for any length of time, and all soils should soon become sterile 
wastes composed essentially of quartz, kaolin and ferruginous 
oxides. It has been suggested that the original mineral particles 
are protected from decomposition by the formation of a coating 
"gel." That is, that silica, alumina, ferruginous or other 
materials result from the decomposition of the minerals in a 
jelly-like form on the surface of the soil grains, protecting them 
from further action of the soil solution.- If diffusion can take 
place through the gel, solution and hydrolysis of the mineral 
would proceed, although the presence of the gel would prob- 
ably retard the rate of the reaction. If it be postulated, how- 
ever, that diffusion through the gel does not take place, the 
minerals of the soil can have no influence On the composition of 
the soil solution, which is an unthinkable alternative. The 
presence of such gels in the soil has frequently been assumed, 
but satisfactory proof is generally wanting. 

In general, the same kind of considerations developed for 
orthoclase hold for the other soil minerals. If minerals of this 
character be pulverized or ground reasonably fine and then be 

' Van Hise, loc. cit., p. 693. 

'A gel is a jelly-like substance, apparently continuous, which forms 
either by the settling from suspension in a liquid of very fine particles 
which then become aggregated ; or, is formed by the evaporation of a 
liquid containing fine particles in suspension until the quantity of liquid 
remaining is just sufficient to serve as a cementation medium holding 
the suspended particles together in a semi-rigid mass. For an experi- 
mental demonstration of the formation of such a gel, see. The effect 
of water on rock powders, by Allerton S. Cushman, Bull. Xo. 92, Bureau 
of Chemistry, U. S. Dept. Agriculture, 1905. 



THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION 37 

shaken with, distilled water which has been previously boiled 
to eliminate the dissolved carbon dioxide, the resulting solution 
will give an alkaline reaction with such indicators as phenol- 
phthalein or litmus.^ If a soil be shaken up thoroughly with water, 
the resulting solution filtered free of suspended matter, as by 
passing through a Pasteur-Chamberland bougie, and then boiled 
to eliminate the carbon dioxide, in the vast majority of cases the 
solution will also give an alkaline reaction with phenolphthalein 
or litmus. The waters of most of our springs, ponds, creeks 
or rivers being natural soil solutions, give an alkaline reaction 
after boiling. 

But the mineral content of these natural waters varies greatly. 
These waters are composed in part of the "run-off," in part of 
a portion of the "cut-oiT" waters, described above. This por- 
tion of the cut-off, normally, in passing through the soil goes 
mainly through the larger interstices. It is not long in contact 
with the individual soil particles and floccules, and because 
diffusion of dissolved mineral substances is quite slow, especially 
in dilute solutions, it takes up but little mineral matter from 
such aqueous films as it may intercept. 

A different state of things exists with that portion of the cut- 
oft" water which returns towards the surface by reason of capil- 
lary forces, to form the great natural nutrient medium for 
plants. This water is moving over the soil particles in films, and 
with slowness. It is long in contact with successive fragments 
of any particular mineral and all the different minerals making 
up the soil. Consequently, it tends towards a saturated solu- 
tion with respect to the mineral mass ; and it follows that if every 
soil contains all the common rock-forming minerals, every soil 
should give the same saHirated solution, barring the presence of 

In making such experiments in the laborator.v or in lecture demon- 
strations, it is well to have the mass of water large in comparison with 
the mass of powdered mineral or rock ; otherwise secondary adsorption 
effects may occur and obscure the results of the hydrolysis. 



38 THE SOIL SOLUTION 

disturbing factors.^ Disturbing factors, however, enter into all 
cases under field conditions, such for instance as the presence 
of some uncommon or unusual mineral in appreciable amounts, 
differences in temperature, surface effects, or extraneous sub- 
stances. These will be considered later, but another disturbing 
factor requires immediate consideration. 

In every soil, varying proportions of the soluble mineral con- 
stituents are present otherwise than as definite mineral species ; 
that is, they are present as solid solutions, or absorlDed on the 
soil grains or perhaps absorbed in some other manner. The con- 
centration of the liquid solution in contact with a solid solution 
or complex of absorbent and absorbed material is dependent 
upon the relative masses of solution and solid. Thus, the con- 
centration of a solution with respect to phosphoric acid, when 
brought into contact with so-called basic phosphates of lime or 
iron, is dependent in a marked way upon the proportion of solu- 
tion to solid." Consequently it is to be expected that an aqueous 
extract of a soil will vary in concentration with the proportion 
of water used ; and that with the same proportion of water, 
different soils or different samples of the same soil will yield 
different concentrations. 

How far absorbed mineral constituents affect the solubility 
of the definite minerals in the soil or influence the concentra- 
tion of the soil solution, it is not possible to predict with any 
approach to certainty. Those soils which hold the most mois- 
ture are generally the best absorbers. Moreover, the soluble 
mineral constituents of the soil, for instance potassium' or 
phosphoric acid, are absorbed to a very high degree from dilute 

^ Feldspars certainly, and phosphorites possibly, are mineral com- 
ponents of the soil ; and these substances when ground sufficiently fine 
have been added to soils with sometimes an increased production of 
crop. Other minerals, such as leucite, have given similar results. But 
also apparently pure quartz sand sometimes accomplishes the same re- 
sults, as fo.r example, in the experiments of Hilgard cited above. It 
has not been shown, however, that the addition of any of these sub- 
stances produces an appreciable change in the concentration of the soil 
solution. 

" The action of water and aqueous solutions upon soil phosphates, 
by Frank K. Cameron and James W. Bell, Bull. No. 41, Bureau of Soils, 
U. S. Dept. of .Agriculture, 1907. 



THE MINERAL, CONSTITUENTS OF THE SOIE SOLUTION 39 

solutions. Consequently it is to be expected that variations in 
the concentration of the natural soil solution would be less than 
in aqueous extracts, when there is employed a constant and rela- 
tively large proportion of water to soil. These considerations 
are of great theoretical importance since they appear to negative 
the possibility of getting, with present experimental resources, 
any exact knowledge of the concentrations of the mineral con- 
stituents in the soil solution when the soil is in condition to grow 
the common crop plants. Moreover, they furnish a guide to 
the limitations which must be recognized in attempting to postu- 
late what these concentrations may be on the basis of analytical 
data obtained from aqueous soil extracts. 

IMany attempts have been made to extract the solution nat- 
urally existing in the soil and to analyze it. The results ob- 
tained have not been very satisfactory, owing mainly to the 
mechanical difificulties involved. As pointed out above, the so- 
lution in a soil under suitable conditions for crop growth is held 
by a force of great magnitude. Nevertheless, by using power- 
ful centrifuges, with saturated soil, it has been possible to throw 
out the excess of solution over the critical water content of the 
soil. In this way small quantities, generally a very few cubic 
centimeters at a time, have been obtained. The analysis of a few 
cubic centimeters of a very dilute solution is in itself difficult, 
involving necessarily more or less uncertainty as to the absolute 
value of the results. Nevertheless, the concentration of the 
soil solutions thus obtained, with respect to phosphoric acid and 
potash, varied but little for soils of various textures from sands 
to clays, and the variations observed could not be correlated with 
the known crop-producing power of the soils. The average 
concentrations of the soil solutions thus obtained lies in the 
neighborhood of 6-8 parts per million (p.p.m.) of solution for 
phosphoric acid (P0O5) and 25-30 parts per million for potash 
(KoO).^ In the following table are given the results obtained 

^ In this connection it is interesting to note that recent investiga- 
tions on the proportions of phosphoric acid, potassium and nitrates in 
cuhural solutions best adapted to the growth of wheat, give the same 
ratio of phosphoric acid to potassium as the figures just cited show- 
to exist normally in the soil solution. 



40 



the; SOlIv SOLUTION 



by analyzing solutions extracted from different samples of loams 
and sands by means of a centrifuge. Tbe crop growing on these 
soils and the crop condition at the time the samples were col- 
lected arc given in the table, and the percentages of water in 
the samples when placed in the centrifuge are also given. 
Analysis of Soil Solution Removed from Fresh Soils 
BY THE Centrifuge. 



Soil 



Leonard town loam 
Leonardtown loam 
Leoiiardtowii loam 
Sassafras loam .... 
Sassafras loam • • • • 
Sassafras loam • • • • 
Sassafras loam . - . . 
Sassafras loam • • • • 
Sassafras loam .... 

Norfolk sand 

Norfolk sand 

Norfolk sand 

Norfolk sand 

Norfolk sand 



Crop 



Wheat 

Wheat 

Wheat 

Clover 

Corn 

Corn 

Wheat 

Wheat 

Corn 

Forest 

Corn 

Wheat 

Wheat 

Corn 



Condition 
of crop 



Good 

Poor 

Good 

Good 

Medium 

Medium 

Good 

Poor 

Good 

Poor 

Good 

Good 

Poor 

Medium 



Per cent 
moisture. 



22. o 
25.2 
17.6 
19.7 

17-5 
18.3 
18.8 
20.0 

17-3 
10.0 
II. 9 
10.7 
1 1.2 
10.6 



Parts per million 
of solution 



6 

10 

8 

5 



/ 
7 
8 

5 
1 1 
18 
8 
9 



17 
9 
22 
18 
13 
83 
44 
27 

24 
18 
36 
45 
38 
65 



19 
38 
19 
36 
25 
34 
24 
25 
3' 
31 
31 
24 
35 



The concentrations of the solutions obtained from the sam- 
ples do not justify any correlation with the crop-producing 
power of the soils, nor with the texture of the soils. The wide 
variation in the concentrations with respect to calcium is prob- 
ably due to the fact that all of the samples came from fields 
which had been limed, some quite recently, and that the con- 
tent of carbon dioxide in the different samples varied. It is of 
special interest to note that the content of calcium in the solu- 
tions does not show any obvious relation to the content of 
phosphoric acid.^ 

An effort has been made to ascertain the rriineral concentra- 
tion of soil solutions as they occur naturally in the field. Be- 
' For the literature of the earlier work on the composition of 
aqueous extracts of soils, see: How crops feed, by Samuel ^\'. John- 
son. 1890, p. 3og et seq.; see also. On the analytical determination of 
probablv availalile "mineral" plant-food in soils, by Bernard Dyer, Jour. 
Chem. 'Soc, 65, 1 15-167, (1894) : and Soils, by E. W. Hilgard, 1906, 
p. 327 ct seq. 



the; minerai, constituknts of the soil solution 41 

cause of the practical impossibility of extracting the actual soil 
solution, an empirical method was employed. Areas were se- 
lected where good and poor crops were growing near each other 
on the same soil types, and preferably in the same field. Sam- 
ples of soil from under these crops were taken at several inter- 
vals during the growing season, cjuickly removed to a nearby 
laboratory, shaken thoroughly with distilled water in the pro- 
portion of one part of soil to five parts of water, allowed to 
stand twenty minutes and the supernatant solution passed through 
a Pasteur-Chamberland filter.^ 

As has been pointed out above, the aqueous extract of a soil 
thus arbitrarily prepared has no definite or causal relation to 
the soil solution in the field. It is certain that the solutions 
would not generally be the same. It should also be emphasized 
that such a procedure can not, as some investigators have as- 
sumed, afford a criterion between soluble and insoluble salts in 
the soil, else the proportion of water to soil used above some 
minimum would be immaterial as far as the amounts which 
go into solution are concerned. The proportion of water to 
soil is not immaterial, however, considering the chemical nature 
of the soil components and the results of experiment. Con- 
sequently, it is clear that the concentration of the soil solu- 
tion is not simply the ratio of the amounts found in the aqueous 
extract, to the percentage of moisture in the soil, but something 
quite different. 

Artificial solutions prepared in the manner described above 
should, however, furnish evidence as to whether or not there 
are recognizable differences in the soluble mineral constituents 
of good and poor soils respectively ; and if such differences exist, 
whether they are consistent. That is to say. if the more pro- 
ductive soils also uniformly yield aqueous extracts of a higher 
concentration, then it would be a fair inference that their natural 
soil solutions are maintained at a higher concentration than in 
the less productive soils. 

^ Capillary studies and filtration of clays from soil solutions, by 
Lyman J. Briggs and Macy H. Lapham, Bull. No. i9» Bureau of Soils. 
U. S. Dept. Agriculture, 1902 ; Colorimetric, turbidity and titration 
methods used in soil investigations, bv Oswald Schreiner and George 
H. Failyer, Bull. No. 3^> Bureau of Soils, U. S. Dept. Agriculture, 1906. 



42 



the; soiIv solution 



Results obtained for several localities and several crops, taken 
from the original records, are given in the following tables.^ 
Water Soi^uble Constituents of Soil. 
Locality, Salem, N. J. Soil type, Norfolk sand. Crop, wheat. 
Yield, good. 





Depth 
inches 


Moisture 
content 
Per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 

(Ca) 


Potassium 

(K) 


March lo 


0-I2 
12-24 
1-24 
1-24 
1-24 


13.2 
"•5 

4-3 
4.6 
9.6 


12 

7 
4 

5 
2 


5 
5 

14 
13 
14 


12 
16 

T 1 








24 







Locality, Salem, N. J. Soil type, Norfolk sand. Crop, wheat. 
Yield, poor. 





Depth 
inches 


Moisture 
content 
Per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid ( PO4) 


Calcium 

(Ca) 


Potassium 

(K) 




0-12 

12-24 

1-24 


12.0 

12.0 

9-3 


II 
10 

A 


5 

3 
00 


"^2 




22 
20 









Locality, Salem, N. J. Soil type. Sassafras loam. Crop, wheat. 
Yield, medium. 





Depth 
iuches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 

(Ca) 


Potassium 

(K) 


March 10 

March 14 

March 20 


0-12 
12-24 

0-12 
12-24 
24-36 

0-12 
12-24 
24-36 

X-24 


23.2 
21.6 
22.3 
20.2 
20.3 

193 
18.6 
12.6 
22.5 


19 
II 
18 

15 
18 

7 
4 
5 

A 


10 

10 

8 

12 

17 
10 
II 
12 
T 1 


8 

14 
18 
21 
16 
21 
21 
21 
21 







^ The chemistry of the soil as related to crop production, by Mil- 
ton Whitney and F. K. Cameron, Bull. Xo. 22, Bureau of Soils, U. S. 
Dept. Agriculture, 1903. 



the; mineral constituents of the soie solution 43 



Locality, Salem, N. J. 



Soil type, Sassafras loam. Crop, grass. 
Yield, fair. 





Depth 
inches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 

(Ca) 


Potassium 

(K) 


March lo 

March 14 

March 31 

April 2 


0-12 
12-24 
24-36 

0-12 
12-24 
24-36 

0-12 
12-24 

0-12 
12-24 
24-36 


25.0 
238 
19.9 
25.8 

23-1 
21.8 

23.0 

21.6 

24.8 

24.0 
21.4 


13 

7 

16 

21 

8 

9 
II 

8 
8 
6 
3 


28 

26 
8 
12 
12 
15 
23 
20 
16 
21 
II 


18 
13 
15 
21 

15 
21 

43 
34 
41 
38 
25 



Locality, Salem, N. J. Soil type, Sassafras loam. Crop, wheat. 
Yield, good. 





Depth 
inches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 

(Ca) 


Potassium 

(K) 


March 17 

March 17 

March 24 

March 26 


0-12 

12-24 

0-12 

12-24 

0-i2 

12-24 

0-12 

12-24 

24-36 

0-12 

12-24 

24-36 

0-12 

12-24 

1-24 

1-24 

1-24 

1-24 

1-24 


22.0 
18.1 
18.3 
18. 1 
. 24.7 
22.3 
234 
23-9 
22.4 

2'?. 6 


8 

8 

ID 

9 

14 

8 

4 

12 

8 

8 


6 
15 
15 
24 
12 
II 
16 
16 

3 
16 

17 
II 

51 
55 
20 
26 

19 
21 

63 


10 

14 

Lost 
25 
30 

38 
16 
20 
21 
30 
47 
38 
23 
32 
13 
14 
22 




244 ' 8 
21.6 ] 8 
5-2 14 
8.0 15 
10.6 2 
IS s ' fi 


Tune 8 






8.2 
15.0 
10.6 


6 
5 
7 




19 

17 







44 



the; soil solution 



Locality, Salem, N. J. 



Soil type, Sassafras loam. 
Yield, fair. 



Crop, clover. 



Parts per million of oven-dried soil 




Locality, St. Marys, Md. Soil type, Leonardtown loam. Crop, wheat. 

Yield, good. 





Depth 
inches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 
(Ca) 


Potassium 

(K) 




0-12 
12-24 

0-12 
12-24 

0-12 
12-24 

0-12 
12-24 

0-12 
12-24 

0-12 
12-24 

0-24 

0-24 

0-24 


21.8 
21.3 
22.2 
21.8 
22.4 
21.8 

17.0 

21.0 

150 

15-9 
14.2 
19.9 
15.0 

15.7 
16.4 


5 
4 
8 

4 
7 
7 
5 
5 
13 
9 
3 
4 
6 

5 

8 


10 

7 

15 

II 

14 
8 
16 
7 
34 
17 
14 
13 
II 

3 
15 


12 
10 
52 
38 
23 
30 
25 
19 
28 
26 
24 
25 
13 
17 
15 


April 29 








August 14 

August 15 

August 15 



THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION 



45 



Locality, St. Marys, Md. Soil type, Leonardtown loam. Crop, wheat. 

Yield, poor. 





Depth 
inches 


Moi.-ture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid (PO4) 


Calcium 

(Ca) 


Potassium 

(K) 


May 14 


0-12 
12-24 

0-12 
12-24 

0-24 

0-24 


14.7 
19.9 
7.8 
14.9 
16.0 
195 


5 
4 
4 
4 
4 
6 


8 

4 

7 

II 

4 
4 


35 
30 
22 




August 14 

August 15 


23 
16 

13 



Locality, St. Marys, Md. Soil type, Leonardtown loam. Crop, corn. 

Yield, good. 





Depth 
inches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid CPO4) 


Calcium 

(Ca) 


Potassium 

(K) 


May 8 


0-12 
12-24 

0-12 
12-24 

0-24 


18.2 
18 9 
18.2 
18.8 
17-5 


9 
10 

3 
6 

7 


12 

7 
24 
19 
30 


29 
26 


May 18 


August 8 


28 
18 



Locality, St. Marys, Md. Soil type, Leonardtown loam. Crop, corn. 

Yield, poor. 





Depth 
inches 


Moisture 
content 
per cent. 


Parts per million of oven-dried soil 


Date 


Phosphoric 
acid(P04) 


Calcium 

(Ca) 


Potassium 

(K) 




0-12 

12-24 

0-24 

0-24 


16.6 

17.4 
19.9 
21.6 


5 
6 

9 

7 


12 

8 

25 

15 




.vidy ^^ 

August 8 

August 15 


22 
20 
13 



It will be observed that the results given in the above tables 
are expressed in parts per million of oven-dried soils, in order 
to have some definite basis of comparison, and because it was 
anticipated at the time the investigation was made that larger 



46 THIi SOIIv SOI.UTION 

quantities of dissolved minerals would be found under the better 
crops, and vice versa. An inspection of the results, however, 
shows that no such correlation can be made, nor in fact can any 
consistent correlation be made between the dissolved material 
and crop, soil type, water content, depth of soil or part of the 
growing season/ It appears, therefore, that in so far as the 
field method of analyzing an arbitrarily prepared aqueous ex- 
tract is competent, there is no evidence that there are important 
characteristic differences in the concentration of the mineral 
constituents in different soil solutions in the field. 

The order of concentration of the soil solution can be approxi- 
mated from the given data, if the assumption be made that in 
the preparation of the aqueous extract, soluble mineral constit- 
uents are of minor importance, other Ithan the constituents 
already dissolved in the soil solution. The calculation is very 
laborious, is not exact, and on account of the assumptions made 
the actual figures obtained are of no especial value in any par- 
ticular case. Remembering the method of making up the solu- 
tions from which these results were obtained, it would be suffi- 
ciently near the truth to assume an average moisture content 
of 20 per cent., when the figures given here for the soil approxi- 
mate those which would be obtained for the soil solution. More 
exact calculations have been made for a large number of such 
cases, and it has been found from this method of estimation 
that the average composition with respect to phosphoric acid 
would be about 6-8 parts per million, and for potash about 
25 parts per million, figures which agree with the results ob- 
tained for the examination of solutions extracted from saturated 
soils by means of the centrifuge. 

^ King, however, claims that the concentration of the soil solution 
with respect to mineral plant nutrients, is higher in the soils of the 
northern states than in the soils of the South Atlantic states. See : 
Some results of investigations in soil management, by F. H. King, Year- 
book, U. S. Dept. Agriculture, 190.^, p. 159-174. Bailey E. Brown has 
obtained some preliminary results which suggest that there may be 
seasonal variations with respect to some of the dissolved mineral con- 
stituents. See, Annual Report of the Pennsylvania State Experiment 
Station, 1908-9, pp. 31 et seq. 



THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION 47 

The results given in the foregoing tables were obtained under 
great difficulties, and in some part the variations they show are 
undoubtedly due to inevitable inaccuracies of analytical work 
done under such circumstances. Some of the variations may 
also be due to the disturbing influences in the soil referred to 
above. Experience has shown, however, that the preparation 
of an aqueous extract of the soil of any particular field is by no 
means a simple matter. Extracts made from samples taken 
within a few feet of one another frequently show variations of 
the same order as with samples from entirely different fields, or 
even soil types. Differences in the preliminary drying out of 
the sample before the addition of the water, seems to result in 
the same order of differences as obtained between different soils. 
In consequence of these facts, and of the further fact that an 
arbitrary aqueous extract of a soil cannot be assumed to repre- 
sent in any definite way the natural soil solution, the results of 
the field examination are inconclusive as to the concentration of 
the soil solution in situ. It is more necessary, therefore, that 
other lines of evidence should be sought as to the mineral char- 
acteristics and concentration of the soil solution. Such a line 
of evidence is found in certain percolation experiments.^ 

If a solution of a soluble phosphate be percolated through a 
soil, a part of the phosphate will be removed from the solution 
and absorbed by the soil ; that is, there will be a redistribution 
of the phosphate between the soil and the water. As the pro- 
cess continues, however, relatively less and less phosphate is 
absorbed by the soil and the concentration of the percolate be- 
comes more and more nearly that of the added solution. This 
absorption takes place more or less closely in accordance with 
the simple law that the absorption of phosphates by the soil, 
per unit of solution which is percolating, is proportional to the 
total amount of phosphate which the soil may yet take from 
that solution if percolated indefinitely. This law is expressed 
by the equation dy/dx ^ K(A — 3') where y is the amount 

^ The absorption of phosphates and potassium by soils, by Oswald 
Schreiner and George H. Failyer, Bull. No. 32, Bureau of Soils, U. S. 
Dept. Agriculture, 1906. 



48 Till; SOIL SOLUTION 

absorbed, .r amount of solution that has passed, and A is the 
total amount which can ultimately be absorbed by that particular 
soil from that particular solution. K is also a characteristic 
constant. ]f the percolation be maintained at constant rate, then 
t, time, can be substituted for .r and the equation becomes 
dy/dt = KiyA — 3'), the ordinary rate equation for a mono- 
molecular reaction of the first order, whether chemical or j^liys- 
ical. 

With such absorptions as are involved in soils, a clay exposes 
a greater amount of absorbing surface than does a loam or sand, 
and it will show the greatest absorption towards any particular 
solution, other things being equal. The curve showing the con- 
centration of percolate would lie lower for a clay than for a 
loam, or for a sand. This is illustrated in the accompanying 
sketch diagram, where y represents concentration of percolate 
and t represents time. 




Fig. I. 

Tf after percolation has proceeded for some time (in some 
experiments for several weeks and until the soil contained i 
or 2 per cent, of phosphoric acid) pure water be passed through 
the soil, then, as soon as the previously used phosphate solution 
has been displaced, the concentration of the percolate drops and 
continues practically constant for an indefinite period. ]\ lore- 
over, no matter what the soil may be as to texture or compo- 
sition, the same concentration of percolate is obtained, namelv, 
6-8 parts per million, the concentration which the soils yielded 
prior to treatment with the phosphate solution. Similar ex- 
periments w^hen the soils were treated with salts of potassium 
have given like results, although the curves obtained from pass- 
ing pure water through the soils do not lie quite so close to- 



THU MINERAL CONSTITUENTS OF THE SOIL SOLUTION 49 

gether; but the concentration of the percolate with respect to 
potassium generally lies somewhere between 25 and 30 parts per 
million. 

The removal of a soluble constituent from the soil by per- 
colating water appears to be described by a rate equation similar 
to that given above for absorption. If the rate of percolation 
be maintained constant this formula is 

d.v/dt = K(B — x) 

where .r is the amount removed by the percolation, with time 
t, K is a constant characteristic for the particular system^ under 
consideration, and B is the total amount of the constituent 
which may ultimately be leached out. In other words, the rate 
in any particular soil will depend upon the amount of the con- 
stituent still absorbed in that soil but has no necessary connec- 
tion with the rate which would hold for the same amount of 
the constituent in any other soil. 

Theoretically, two consequences follow frcjm this law which 
require consideration here. The rate at which a constituent is 
removed gradually becomes less as percolation proceeds. If the 
soil contains an amount of the constituent approaching the total 
amount wdiich it can absorb, as for instance is probably the case 
sometimes when large applications of lime have been made to the 
soil, the concentration of the percolating solution might be ex- 
pected to change noticeably. Generally, however, a soil con- 
tains nowhere near as much phosphoric acid or.potassium as it 
is capable of absorbing, so that the concentration of the percolat- 
ing water changes but very little with respect to these constit- 
uents. It follows from the equation that if, percolation con- 
tinues uninterrupted, the concentration of the percolate, so far 
as it is determined by an absorbed constituent, must get less 
and less until it becomes a vanishing quantity. This state of 
affairs does not exist in the soil, however, for percolation by 
pure water does not continue uninterrupted for any length of 
time. The rise of the capillary water in the soil will, under 
normal conditions, enable the soil to reabsorb more of the or- 
dinary mineral constituents than is removed by percolating 



50 



THE SOIL SOLUTION 



waters. Further attention will be given the matter in another 
chapter. 

Another but quite different line of evidence as to the probable 
concentration of the soil solution is furnished by the investiga- 
tion of the solubility of certain phosphates.^ It is popularly 
supposed that when superphosphate containing mono-calcium 
phosphate, CaH4(POj2-H20, is added to a soil there is a more 
or less permanent increase of readily soluble phosphoric acid in 
the soil, although a part "inverts" to the somewhat less soluble 
dicalcium phosphate, CaH(P04).2H„0. Such probably is far 
from a correct view of what actually takes place. The results 
obtained by studying the solubility of the different lime phos- 
phates in water at ordinary temperature (25° C.) can be ex- 
pressed in a diagram similar to the accompanying sketch, which 
is much distorted for convenience in lettering. As the diagram 
indicates, when the concentration of the solution increases with 
respect to phosphoric acid, the lime is at first less and less solu- 
ble until the point represented by B is reached, then becomes 
more and more soluble until the point D is reached, from then 
on becoming less and less soluble, until the solution reaches a 



c 







^ 


c 




y^ \ 




a 


y 


/ ^E 


Vl. 




P2O5 in solution 



Fig. 2. 

syrupy consistency. In contact with all solutions represented 
by points on the line DB the stable solid substance which can 

^ For reference to the literature and detailed discussion see : The 
action of water and aqueous solutions upon soil phosphates, by F. K. 
Cameron and J. M. Bell, Bull. No. 41, Bureau of Soils, U. S. Dept. 
Agriculture, 1907. 



THE MINERAL CONSTITUENTS OF THE SOIE SOLUTION 5 1 

exist is mono-calcium phosphate, CaH^(P04)2.H20. Along the 
line CD the only solid which is stable and can continue to per- 
sist is the dicalcium phosphate. From the point C the composi- 
tion of the stable solid varies continuously with the concentra- 
tion of the liquid solution. Therefore, these solids form a 
series varying in composition from pure dicalcium phosphate 
to pure calcium hydroxide. One of these basic phosphates, as 
they would ordinarily be called, has a less solubility than any 
other, as indicated by the point B. All solutions to the right of 
the point B have an acid reaction, while all solutions to the left 
possess an alkaline reaction. It follows from these facts that 
if we start with any lime phosphate corresponding to some 
point to the right of B and dilute it, or what amounts to 
the same thing in case it has been added to the soil, if we 
leach it, phosphoric acid will go into solution more rapidly 
than will lime until the composition of the residue is that of 
the basic phosphate stable at B. Similarly, if we start with a 
phosphate more basic, lime will be removed more rapidly than 
phosphoric acid, until the residue has the composition of the 
phosphate of lowest solubility. From this point, with continued 
leaching, the lime and phosphoric acid will dissolve in a definite 
ratio, which ratio is obviously that of the phosphate of least solu- 
bility. That is to say, if the leaching process is slow, as would 
be the case under soil conditions, the solution would have a 
perfectly definite concentration with respect to lime and phos- 
phoric acid. What the ratio of lime to phosphoric acid may 
be, is of no particular interest in this connection, but the order 
of concentration of phosphoric acid is of interest. Owing to 
serious analytical difficulties, this has not yet been determined 
with any great precision, but by interpolating on the experiment- 
ally determined curve AC, this concentration is found to be some- 
where in the neighborhood of 5-10 parts per million, figures 
close to those obtained for the concentration of the soil solution 
with respect to phosphoric acid by the previously described in- 
vestigations. 

Under ordinary circumstances, however, it is not probable that 
lime is the dominant base controlling the concentration of phos- 



52 THE SOIL SOLUTION 

phoric acid in the soil solution, since the great majority of ag- 
ricultural soils contain vastly more ferric oxide (more or less 
hydratcd) than is equivalent to any amount of phosphoric acid 
that will ever be brought into the soil ; and ferric phosphates are 
less soluble relatively than lime phosphates. Investigation of 
the relation of ferric oxide to solutions of phosphoric acid shows 
that the system is quite similar in many respects to the basic 
lime phosphates and water just described. When the ratio of 
iron to i)hosphoric acid in the solid is greater than that required 
by the formula of the normal phosphate, FePO^, the aqueous 
solution will have an acid reaction and contain a mere trace of 
iron and an amount of phosphoric acid determined by the com- 
position of the solid and by the proportion of solid to water. 
The basic ferric phosphates seem to be solid solutions which 
yield a very dilute aqueous solution when brought into contact 
with water. What the concentration will be under soil condi- 
tions is shown by the percolation experiments cited above. 

The addition of other substances will in many cases affect 
more or less the solubility of the soil minerals. If these sub- 
stances be electrolytes, they will generally, but not always, afifect 
the solubility of the minerals as would be anticipated from the 
hypothesis of electrolytic dissociation. Thus, the addition of 
potassium sulphate lessens the solubility and hydrolysis of a 
potash feldspar or a potash mica. Contrary, however, to the 
indications of the hypothesis, sodium nitrate decreases the solu- 
bility of a ferric phosphate. While appreciable solubility effects 
take place with sufficiently high concentrations, laboratory ex- 
periments indicate that the addition of such substances, even in 
a liberal application of fertilizers, is not sufficient to produce 
any great effect on the concentration of the soil solution. Simi- 
larly, it has often been supposed that the ammonia, and nitrous 
and nitric oxides of the atmosphere carried into the soil by rain, 
or formed in the soil by bacterial action, affect the solubility of 
the soil minerals, but it is highly improbable that the concentration 
with respect to these agents ever becomes sufficiently high, as 
laboratory investigations show to be necessary to affect appreci- 
ably the solubility of the ordinary rock- or soil-forming minerals. 



the; mineral constituents op' the soie solution 53 

Rain brings from the atmosphere into the soil two agents, 
however, which do markedly affect the solubility of the soil min- 
erals, namely, oxygen and carbon dioxide. The atmosphere 
within the soil contains normally a somewhat smaller proportion 
of oxygen than does the air above the soil. Rain in falling 
through the air absorbs or dissolves relatively more oxygen than 
nitrogen. Therefore when the rain water has penetrated the 
soil to any considerable depth there should be, and probably is, 
a liberation of dissolved oxygen into the atmosphere of the soil 
interstices. This dissolved oxygen in becoming liberated or when 
dissolved in the film water appears to be especially active to- 
wards the ferrous or ferro-magnesian silicates. These minerals 
are, moreover, as a class probably the most soluble of the rock- 
forming silicates. Consequently oxygen brought into the soil 
in this manner is one of the most important agencies in breaking 
down and decomposing such minerals as the amphiboles, pyrox- 
enes, chlorites. certain serpentines, phlogopites and biotites ; at the 
same time there is formed ferric oxide (more or less hydrated) 
and silica (probably as quartz) and magnesium, potassium, cal- 
cium or sodium pass into solution, probably as bicarbonates. 
That the concentration of the soil moisture may thus be made 
temporarily abnormal is not impossible, though scarcely prob- 
able. 

The soil atmosphere has normally a decidedly higher content 
of carbon dioxide than the atmosphere above the soil. Conse- 
quently the soil water is always more or less "charged" with 
carbon dioxide, and the presence of the carbon dioxide decidedly 
augments the solvent powers of the water towards a great many 
and different kinds of rock-forming or soil minerals.^ 

What the mechanism of the reaction may be is far from clear. 

^ For references to the literature see Bull. No. 3°. Bureau of Soils, 
U. S. Dept. of Agriculture : also. The action of carbon dioxide under 
pressure upon a few metal hydroxides at 0° C, by F. K. Cameron and 
W. O. Robinson, Jour. phys. chem., 12, 561-573, (1908) ; The influence 
of colloids and fine suspensions on the solubility of gases in water, 
Part I. Solubility of carbon dioxide and nitrous oxide, by Alexander 
Findlay and Henry Jermain Maude Creighton, Trans. Chem. Soc, 97» 
536-561, (1910). 



54 THE SOIL SOLUTION 

The obvious explanation, at least in the case of the ordinary 
silicates of the alkalis or alkaline earths, is that by forming bi- 
carbonates of the hydrolyzed bases, the active mass of the re- 
action product with water is decreased and hydrolysis thereby 
increased. But this explanation is apparently insufficient to ac- 
count for the effects sometimes observed. It has been shown 
that the passage of carbon dioxide through solutions of the 
silicates, will produce more or less slowly a precipitation of silica, 
and there seems little reason to doubt that it does induce to 
some degree a decomposition and consequent greater solubility 
of the silicates of the alkalis and alkaline earths. It also in- 
creases to an appreciable extent the solubility of the phosphates 
of iron, alumina, and lime. Therefore, the variation in the con- 
tent of carbon dioxide in different soils, and its continual varia- 
tion from time to time in any one soil, must be expected to pro- 
duce corresponding changes in the soil solution with respect to 
such bases as potassium and lime, and also with respect to phos- 
phoric acid. This has been verified experimentally with aqueous 
extracts of soils, the solutions being charged with carbon dioxide 
while in contact with the soils. ^ It is not conceivable, however, 
that any great difference can exist in the partial pressures of 
carbon dioxide in different soils which are in a condition to 
support crops, and therefore great absolute differences in the 
mineral content of the soil solution are not to be anticipated, 
nor are they actually observed. 

It has long been held that the organic substances in the soil 
have an important solvent effect on the minerals. This assump- 
tion seems quite unwarranted in the light of our present know- 
ledge, although it is not to be denied that occasionally there 
may be present in the soil some soluble organic substance which 
influences the mineral content. Generally it has been assumed 
that the effective organic substances influencing the solubility 
of the minerals are organic acids, of which a number have found 
their way into past and even current literature, and which have 
* See, for instance, the results obtained by Peter, Proceedings of the 
igth Annual Convention of the Association of American Agricultural 
Colleges and Experiment Stations, Bull. No. 164, Office of Experiment 
Stations, U. S. Dept. Agriculture, 1906, p. 151 ct seq. 



the; minerai, constituents oe" the sou, solution 55 

been designated as humic, ulmic, crenic, apocrenic, azohumic 
acids, etc. Their existence has been predicated upon two facts : 
First, humus is soluble in alkaline solutions but is more or less 
completely reprecipitated on the addition of an excess of a strong 
mineral acid, a phenomenon also characteristic of many organic 
acids. But many other organic substances than acids are also 
soluble in the presence of alkalis and insoluble in the presence 
of an excess of strong mineral acids. Second, organic-copper 
complexes have been obtained from humus constituents, and 
supposed to be copper salts of various humus acids. The de- 
scriptions of these complexes so far given do not show that they 
met the usual criteria for definite compounds, but indicate on 
the contrary that they were the results of absorption or possibly 
adsorption phenomena. Consequently the existence of "humic" 
acids is purely hypothetical and without experimental or other 
scientific verification, and calls for no further consideration here. 
It is a widespread and popular notion that substances with 
a slight solubility also dissolve slowly, and that consequently 
the solubility of the minerals in the soil water must necessarily 
be a very slow process. This is, however, a misapprehension. 
It has been shown with a number of the common rock-forming 
minerals, that if they be powdered and then stirred into a rela- 
tively small volume of water, they dissolve very rapidly at first, 
and in a very short time, generally a few minutes, the solution 
is nearly saturated \vitli respect to the mineral. Complete sat- 
uration, however, may require many days. The general shape 
of curve expressing the rate of solubility is shown in the ac- 
companying figure.^ For soils, this fact has been verified re- 
peatedly, in the following way : A cell fitted with parallel elec- 
trodes is placed in circuit with a slide-wire- or WReatstone 
bridge in such a manner that the resistance ol the cell contents 
can be quickly determined. Distilled water is then placed m 
the cell and its resistance found. Generally this will be up- 
1 See, for example, Umwandlung des Feldspats in Sericit (Kali- 
glimmer) von Carl Benedick, Bull. Geol. Inst. Upsala. 7. 278-286, (1904)- 
' See Electrical instruments for determining the moisture, tem- 
perature and soluble salt content of soils, by L. J. Briggs, Bull. No. 15. 
and the electric bridge for the determination of soluble salts in soils, 
by R. O. E. Davis and H. Bryan, Bull. No. 61, Bureau of Soils, U. S. 
Dept. Agriculture. 



5^^ 



THIv SOIL SOLUTION 



wards of loo.ooo ohms. The soil or rock powder under ex- 
amination is then added to the cell, being rapidly stirred into 
the water contained therein. The resistance drops to about 
5,000 ohms within a short space of time, usually three or four 
minutes. A further slight drop in the resistance generally takes 
p»lace, but it requires days, and sometimes even months to be- 
come more than l)areh- appreciable. Tn this manner it has been 




shown that the soil and many of the common soil minerals 
dissolve quite rapidly if they are sufificiently fine to offer a large 
surface to the. action of the water. It would seem to follow, 
therefore, that in the case of the soil solution the concentra- 
tion with respect to these constituents derived from the soil 
minerals, will be rapidly restored whenever disturbed through 
absorption by plants, leaching, or otherwise. 

That the minerals of the soil, or a powdered mineral or rock- 
powder, will dissolve continually as the concentration of the so- 
lution in contact with it is disturbed by abstraction of a dis- 
solved mineral substance, has been shown by numerous experi- 
menters. An apparently obvious way to test this point would lie 
to treat the soil sample ^vith successive portions of water, anO 
to analyze the successive portions for the dissolved mineral sub- 
stances. This method, however, involves serious experimental 
difficulties, owing to the smaller sized mineral particles being 
suspended in the mother liquor, thus precluding satisfactory de- 
cantation and clogging filters. Moreover, such a process in no 
case simulates field conditions. To meet these difficulties, the 
soil or mineral powder has been placed between two porous 



THE MINERAL CONSTITUENTS OF THE SOIE SOLUTION 57 

media, as in the space between two concentric cylinders of un- 
glazed porcelain, the space being closed by a rubber stopper. 
To the interior cylinder is fitted a stopper carrying a tube of 
insoluble metal, such as platinum or tin. This tube is bent into 
a goose-neck form, and just below the stopper the tube is per- 
forated with a small opening. The whole apparatus is filled 
with water and set in a beaker, also filled with water. The metal 
tube is made the cathode in an electric circuit, a platinum or 
other suitable anode being introduced into the beaker. In a few 
minutes the dissolved and hydrolyzed bases pass into the cathode 
chamber, and as the water also accumulates in the chamber by 
electrolytic endosmosis, a solution of the bases dissolved from 
the soil minerals drops from the end of the metal goose-neck. 
By adding water to the outer beaker from time to time, a steady 
stream of alkaline solution has been obtained for months, and 
in no case yet has a soil thus treated failed to continue to yield 
up the bases it contains in its mineral particles. The acids, such 
as phosphoric acid for example, are of course found in the 
water outside the porous cells, and in the case of the phosphoric 
acid it also appears to continue indefinitely to be withdrawn from 
the soil.^ It thus appears that as the products of solution and hy- 
drolysis are removed, by such an endosmotic device as that just 
described or by the roots of growing plants, by leaching or other- 
wise, the soil minerals will continue to dissolve. 

The foregoing arguments as to the concentration of the soil 
solution with respect to those constituents derived from the soil 
minerals, are based on the generally recognized principle that a 
material system left to itself tends towards a condition of stable 
equilibrium or final rest, that is, a condition where such changes 
as are taking place are so balanced that no change occurs in 
the system as a whole. But the soil is a system, continually 
subject to outside forces and influences, and as pointed out 
above, is of necessity a dynamic system. It is doubtful in the 
extreme if any soil in place is ever in a state of final stable 
equilibrium. It would be natural, therefore, to expect and to 

* For detailed description of the apparatus and experimental data, 
see Bull. No. 30, p. 27, et scq., Bureau of Soils, U. S. Dept. Agriculture. 
5 



58 THK soil, SOLUTION 

find that even if the sohition in the soil were dependent on the 
sohibihty of the soil minerals alone and were continually tend- 
ing towards a definite normal concentration, actually this con- 
centration would seldom if ever be realized. Most important in 
this connection is the fact that the concentration of the soil so- 
lution is always dependent in some degree upon the concentra- 
tion of the soluble constituents in the solid phases in other than 
definite chemical combinations. Other factors affecting the con- 
centration of the mineral constituents in the soil solution are 
always existent, and theoretically at least, can not be ignored. 
Nevertheless a priori reasoning as well as the experimental 
evidence at hand indicates that the various processes taking place 
in the soil as a whole continually tend to form and maintain a 
normal concentration of mineral constituents in the soil solution. 



Chapter VIII. 

ABSORPTION BY SOILS. 

A property of soils, affecting profoundly the composition and 
concentration of the soil solution, is absorption.^ It is generally 
recognized that soils are good absorbers for vapors, and this 
fact finds practical expression in the common practice of bury- 
ing things with a disagreeable odor, such as animal carcasses, 
night-soil, etc. It is also well-known that dissolved as well as 
suspended material can be more or less completely removed from 
water by passing it through sand or soil, and this fact finds 
important application in water supplies for cities and towns, 
sewage disposal, etc. It was known as long ago as Aristotle's 
time that ordinary salt is partly removed from water by passing 
through sand or soil. In recent times the practical as well as 
theoretical importance of this phenomenon has led to consider- 
able study and experimental research, so that our knowledge of 
absorption effects is now fairly extensive, though it can hardly 
be claimed that it is satisfactory. The absorption of a dissolved 
substance from solution by a soil may be one or more of at least 
three kinds of phenomena. It may be a mechanical inclusion or 
trapping, distinguished by the term imbibition, the most familiar 
and striking case being the absorption of water itself by soil or 
sponge or similar medium. It may be a partial taking up of 
the dissolved substance to form a new compound or a solid 
solution,' as probably is the absorption of phosphoric acid by 

' For a detailed discussion and citations of the literature, see : Ab- 
sorption of vapors and gases by soils, by H. E. Patten and F. E. Galla- 
gher, Bull. No. 51; and Absorption by soils, by H. E. Patten and W. H. 
Waggaman, Bull. No. 52, Bureau of Soils, U. S. Dept. Agriculture, 
1908. 

' That is, a homogeneous solid, which may be either crystalline or 
amorphous. Probably the readiest criterion for distinguishing between 
a definite compo.und and a solid solution, is that the former is stable 
in contact with a liquid solution of its constituents over a measurable 
range of concentrations, while the composition of the solid solution 
changes with every change in the concentration of the liquid solution in 
contact with it. 



6o the: soil, solution 

lime or ferric oxide. Or it may be a condensation or concentra- 
tion of the dissolved substance on or about the surface of the 
absorbing" medium, a phenomenon known as adsorption. To 
prove tlie existence of adsorption definitely and conclusively in 
any given case is always difficult, if ever possible, but the exis- 
tence of this phenomenon is the most logical explanation of many 
observations, and is generally admitted by chemists and physicists 
at the present time.^ It is by adsorption, probably, that potash 
and ammonia are held by the soil when added in fertilizers. 

That absorption is dependent in some manner upon the solu- 
bility of the dissolved substance in the particular solvent em- 
ployed would seem to be obvious. But what the relation may 
be, if it exists at all, is not known. For instance, silk absorbs 
picric acid from solutions in water and alcohol but not from solu- 
tions in benzene, although the solubility of picric acid in benzene 
lies between its solubility in water and in alcohol. - 

The absorption of any. given dissolved substance from differ- 
ent solvents is markedly different. Most soils absorb methylene 
blue from aqueous solutions Avith great avidity, but washing 
out the absorbed dye with water is an extremely tedious and un- 
satisfactory process, although the dye can be readily and more or 
less completely removed from the soil by alcohol. As might be 
anticipated from this, it is known that the presence of one dis- 
solved substance affects the absorption of another, but in what 
way can not, generally, be anticipated, although it would seem 
that the importance of this subject for manurial practice would 
invite further research. 

From the same solution, dift'erent absorbents remove a dis- 

^ A clear and apparently indisputable case of adsorption has been 
noted by Patten (Some surface factors affecting distribution. Trans. Am. 
Electrochem. Soc, lo, 67-74, (1906). On adding powdered quartz to an 
aqueous solution of gentian violet, there is a distribution of the dye 
between the water and the quartz. A microscopic examination of the 
latter showed that the dye was concentrated in thin layers upon the sur- 
face of the quartz grains, from which it could be washed with water, no 
change in the quartz grains being noticeable. 

" Absorption of dilute acids by silk, by James Walker and James R. 
Appleyard, Jour. Chem. Soc., 69, 1334-1349, (1896). 



ABSORPTION BY SOILS 6l 

solved substance in different degrees. Speaking generally, 
paper absorbs dyes more readily than do soils, while soils ab- 
sorb bases more readily than does paper. Hence the redden- 
ing of litmus paper when in contact with a moist soil. Heavy 
soils or soils containing much hydrated ferric oxide absorb bases 
more readily than do light soils, but this is probably owing to 
relative amounts of surface exposed, for the same relation holds 
true with respect to phosphoric acid. Soils rich in humus are 
better absorbers than soils not so rich. But here again there is 
yet doubt as to whether the explanation lies in the amount or in 
the kind of surface acting. 

Fiom the same solvent different dissolved substances are ab- 
sorbed cjuite differently by any given absorbent. This can be 
readily illustrated again by dyes. H an aqueous solution of a 
mixture of methylene blue and sodium eosine, for instance, be 
shaken up with a soil, or percolated through a column of soil, 
the methylene blue is absorbed the more quickly and completely 
and a partial separation of the two dyes can be readily effected, 
the separation being more or less complete according to the 
conditions of the experiment. In the same manner two salts in 
solution can be separated partially at 'least. ^ Soils absorb po- 
tassium more readily than sodium ; magnesium more readily than 
lime; and ammonia more readily than any of these bases. - 

The absorption from aqueous solutions of inorganic salts in- 
volves a most interesting complication. Just as a mixture of 
two or more dyes or salts in solution can be separated by the 
selective action of an absorbent, so can an electrolyte itself be 
decomposed or resolved. Thus, if a solution of potassium 

^ For a number of interesting examples, see, Ueber das Aufsteigen 
von Salzlosungen in Filtrirpapier, von Emil Fischer und Edward Schmid- 
mer, Liebig's Annalen der Chemie, 272, 156-169, (1893). 

" The prompt absorption of a base by soils is shown by the follow- 
ing experiment : To some freshly boiled distilled water add several 
drops of alcoholic phenolphthalein, and then just enough base to produce 
a decided red color. If the solution be now passed through a short 
column of soil, cotton, shredded filter-paper or similar absorbent, the 
percolate will be perfectly colorless. The red color will be restored, 
however, by adding a little of the base to the percolate. 



62 • THE SOIL SOLUTION 

chloride be passed tlirough a column of soil, or cotton, or paper, 
or any similar absorbent, the filtrate will not only be less con- 
centrated than the original solution, but the potassium will be 
found to have been absorbed to a greater extent than the 
chlorine, that is, the percolate contains free hydrochloric acid. 
The importance of this phenomenon for the conservation of the 
desirable constituents of manurial salts, and the elimination or 
leaching out of the less desirable constituents is obviously great. 
Equally great perhaps, is the effect upon the reaction of the 
soil, whether it be rendered temporarily alkaline or acid, an 
effect of the very greatest importance for the growth of some 
of our common crop plants^ and for the lower soil organisms, 
such as the bacteria, molds, together with ferments, enzymes, 
etc., many of which are very sensitive to the reaction of the 
media in which they may be, and which in turn are of undoubted 
importance in determining the fertility of the soil for higher 
plants. 

The absorption of a dissolved substance from solution by an 
absorbent is in effect a distribution phenomenon and the simplest 
formula to give quantitative expression to such a distribution is 
C/C^ = K when C is the concentration in the liquid phase and 
C^ the concentration in the solid phase, K being a characteristic 
constant for the particular case under consideration. When a 
chemical reaction or a change of state, chemical or physical, is 
involved in the absorption in either dissolved substance or ab- 
sorbent the formula becomes C /C^ = K when n is a function 
which may be very simple or very complex. Attempts to develop a 
precise formula of this general type for the absorption by some 
given soil, although such a formula would be desirable for 

^ See, The toxic action of acids and salts on seedlings, by F. K. 
Cameron and J. F. Breazeale, Jour. Phys. Chem., 8, 1-13, (1904). It is 
quite conceivable, for instance, that if the drainage conditions were not 
exceptionally good under a heavy type of soil, it might be rendered 
temporarily unfit for clover or alfalfa by a heavy application of potas- 
sium salts or of sodium nitrate. The idea put forv^ard by some authori- 
ties that too long continued or over fertilizing renders soils acid, may 
have better foundation than their theoretical reasoning would seem to 
warrant. 



ABSORPTION BY SOILS 63 

theoretical and practical reasons alike, have uniformly failed. 
A sufficient reason for this failure seems to He in the fact that 
most dissolved substances produce an appreciable effect on the 
granulation or flocculation of the soil particles, which is pro- 
gressive with the absorption so that a continual change of ab- 
sorbing or effective surface is taking place as the absorption 
proceeds.^ Moreover, in the case of an absorption, with the 
formation of a continuous film of the dissolved substance, a new 
kind of absorbing surface is developed. Hence n is a func- 
tion of so difficult a character as to defy thus far any attempt at 
formulation." 

We cannot therefore predict in any quantitative way what 
will be the distribution of a soluble substance such as salts in 
commercial fertilizers, for instance, between the solid soil 
particles and the soil solution. Empirical experiments show, 
however, that with the amount of a soluble salt present under 
normal conditions in a humid climate, or as used in fertilizer 
practice, the absorption of ammonia, lime, potassium or phos- 
phoric acid is relatively very great, and in a general way in 
about the order named. 

Absorption is not an instantaneous process. However, the 
rate at which a dissolved substance is absorbed is generally quite 
rapid. That is, if a soil be stirred or mixed with an aqueous 

' That mineral fertilizers have a decided influence on the granula- 
tion of soils and the properties dependent thereon, and that this is of 
practical importance, is gradually coming to be recognized: see, for 
instance, Ein Beitrag zur Kenntnis der Wirkung kiinstlicher Diinger auf 
die Durchlassigkeit des Bodens fiir Wasser, von Edwin Blanck. Landw. 
Jahrb., 38, 863-869, (1909), and the literature there cited. Dr. R. O. 
E. Davis in a yet unpublished investigation has shown that the addition 
of soluble salts produces decided effects upon the soil-moisture rela- 
tions which affect crop production. The critical moisture content is dis- 
placed, the penetrability, permeability, specific volume, vapor tension, 
etc., are affected in measurable degree, and it appears that the physical 
functions of mineral fertilizers are much greater in amount and im- 
portance than has been popularly assumed. 

- The distribution of solute between water and soil, by F. K. Cam- 
eron and H. E. Patten, Jour. Phys. Chem., ", 58i-593, (iQO/)- 



64 THE SOIL SOLUTION 

solution, the absorption takes place very quickly, in the absence 
of any outside disturbing influences. The law governing the 
rate of absorption by soils has not therefore possessed any great 
practical interest and has not been studied from a quanti- 
tative point of view, although it is known qualitatively that the 
rate is increased by increasing the concentration of the solution, 
or by increasing the amount of the absorbent or at least its 
effective surface. Two rate equations are of interest in this con- 
nection, and have been carefully studied. The rate at which a 
salt or other dissolved substance will advance into an absorbing 
soil from a solution is given by the same equation as that describ- 
ing the rate of advance of the water itself, y" =^ kt where y is 
the distance and t the time.^ The constants ;; .and k for 
the slower moving dissolved substance are different from those 
for the water. This equation has probably little importance for 
ordinary agriculture, for absorption by the soil from a large (and 
relatively illimitable) mass of solution is unusual. That it may 
have considerable importance in seepage, irrigation, and some 
soil engineering problems, seems quite likely. 

The rate at which a soil will absorb a dissolved substance from 
a percolating solution is given by the equation dx/dt = K(A — 
.f), as has been pointed out above.- More interesting and im- 
portant, however, is the fact that this same equation describes 
the rate at which an absorbed substance is removed from the 
soil by leaching. In the case of soils in humid areas dx/dt 
rapidly becomes exceedingly small as .r approaches A, that is, 
when the amount of soluble material in the soil becomes small, 
and is practically constant under such conditions, as has been 
pointed out above when describing the removal of potassium 
and phosphoric acid from soils by percolating waters. This 
formula has a special interest in considering the reclamation of 
alkali lands by underdrainage, a problem to which reference 
will be made later. 

Both percolation experiments, as those cited above, and direct 
absorption experiments made by shaking up soils with solutions 
1 See formula, page 28. 
- See formula, page 47. 



ABSORPTION BY SOILS 65 

of the salts in question, show conclusively that the absorptioix 
phenomena taking place in the soil are in harmony with the direct 
solubility effects in tending to produce and maintain a solution 
of a normal concentration as regards those constituents which 
it happens are also derived from the soil minerals.^ It is an 
interesting coincidence that nitric acid (in combination with 
various bases of course) is very little absorbed by most soils, and 
does vary in concentration, not only in different soils but in the 
same soil, between wide limits, and within short intervals of 
time.- The nitrates of the soil are not derived from minerals, 
and should more properly be considered with the organic con- 
stituents of the soil solution. 

An important application of these views concerning absorp- 
tion arises in connection with certain widespread notions con- 
cerning soil acidity. There is a popular belief that most soils 
are acid, that the soil solution contains some free acid, mineral 
or organic, other than dissolved carbon dioxide, and that a 
neutral or alkaline solution is necessary to the successful pro- 
duction of most of our crops. This belief is, however, un- 
warranted, for the vast majority of soils yield an aqueous extract 
which is alkaline when boiled to expel carbon dioxide, and some 
of our crops, for instance wheat, seem to thrive better in a 
slightly acid medium. This popular fallacy seems to have its 

* An extreme case is worth citing in this connection. Mr. W. H. 
Heileman in studying the influence of various kinds of alkali upon plant 
growth, added from 3-4 per cent, of sodium carbonate to soils known to 
be otherwise free from alkali. Wheat seedlings grown in the soils so 
treated showed no ill effects from the added salt. When distilled water 
was percolated slowly through the soils, or shaken up with them, the 
resulting solution contained the merest traces of the alkali. 

The ordinary method of determining the lime requirement of a soil 
by adding lime water until the solution shows an alkaline reaction, is 
another obvious absorption phenomenon, and is not dependent, as popu- 
larly supposed, upon the presence of acids in the soil. Soils which by 
no possibility could contain any free acid, frequently absorb very large 
amounts of lime in this manner. 

' Usually, in the growing season, the soil solution has a much 
higher concentration with respect to nitrates in the morning than it 
has in the evening. 



66 THE SOIL SOLUTION 

origin in the fact that most soils when moistened and pressed 
against blue litmus paper, redden it. This reddening may some- 
times be due to the actual presence of some acid, or to dissolved 
carbon dioxide, but is undoubtedly due in the majority of cases 
to selective absorption. Litmus is a red dye of an acid-like 
character, which forms a soluble blue salt with the ordinary 
bases. But it has been shown that most soils are better ab- 
sorbents of bases than is paper, whereas paper is a better ab- 
sorbent of dye, speaking generally, than is a soil. Consequently 
when moist soil is brought into contact with wetted blue litmus 
paper the base is absorbed more readily by the soil, and the dye 
by the paper, the latter therefore becoming reddened. 

The reddening of blue or "neutral'' litmus paper can be ac- 
complished with various absorbents. By pressing the litmus 
paper between moistened wads of absorbent cotton the redden- 
ing can be readily accomplished, usually in the course of ten 
minutes to a half hour. That the phenomenon is not due to any 
adhering acid on the cotton can be shown in the following way : 
A litmus solution is carefully prepared so that there is a very 
small excess of base present over that required to give the blue 
color. A wad of absorbent cotton is carefully washed by re- 
peatedly sousing it in distilled water from which carbon dioxide 
has been expelled by boiling. When the cotton has been thor- 
oughly washed, it is stirred thoroughly in a portion of distilled 
water, free from carbon dioxide, then withdrawn by some ap- 
propriate instrument and allowed to drain for a few minutes. 
The litmus is added in fairly large quantity to the drainings, 
which should then have a blue color. Again stir the cotton in 
the water, and more or less quickly, depending on the amount 
and purity of the litmus preparation as well as the quantity of 
cotton used, the solution will become red. The only criterion 
for determining surely that a soil is acid, is to make an aqueous 
extract, expel the dissolved carbon dioxide by boiling, or by 
passing through the solution an inactive gas, such as nitrogen, 
and then to test the reaction of the solution. Acid soils un- 
doubtedly do exist, but they are by no means common or wide- 
spread, and are to be regarded as exceptional and abnormal. 



ABSORPTION BY SOILS 67 

The phenomena of selective absorption suggest the important 
part which surfaces play in modifying and changing chemical 
reactions/ For instance, Becquerel- observed that a solution of 
copper nitrate or cobalt chloride diffusing from a cracked test- 
tube placed in a solution of sodium sulphide, led to the forma- 
tion of the corresponding sulphide, but in the crack the metal 
itself was precipitated. Experiments of Graham^ show that 
when a solution of silver nitrate is percolated through charcoal, 
not only is there a selective absorption as is shown by the per- 
colate containing free acid, but there is a chemical reaction 
involved, since the silver is deposited in metallic spangles in the 
interstices of the absorbent. Graham has shown, and since his 
time others, that often metals can be separated from solutions 
of their salts by such absorbents as charcoal. Spring* has 
shown that at bounding surfaces of dilute solutions, chemical 
action is increased. 

It has been shown that the amount and kind of surface has a 
marked influence on the decomposition of hypochlorous acid, 
carbon dioxide, phosphine, arsine, and other compounds. Meyer 
and his associates, as well as a number of other investigators, 
have shown that the character of the surface of the containing 
vessel greatly affects the combination of hydrogen and oxygen. 
Many reactions have been investigated by van't Hoff, who con- 
cludes that both the nature and amount of surface exposed have 
an influence. The inversion of sugar is affected by the nature 
of the walls of the containing vessel, and its reduction by Fehl- 
ing's solution is affected both by the walls of the vessel and 
the amount of cuprous oxide formed in the reaction. Altera- 
tion in the character as well as degree of a number of reactions 
by having them take place in capillary spaces has been observed 

^ For references to the literature see, Bull. No. 30, Bureau of Soils, 
U. S. Dept. Agriculture, p. 61 et seq. 

- Xote sur les reductions metalliques produites dans les espaces ca- 
pillaires, par J\I. Becquerel, Comptes rendus, 82, 354-356, (1876). 

' Effects of animal charcoal on solutions, by T. Graham, Quart. 
Jour. Sci., I, 120-125, (1830). 

' Uber eine Zunahme chemischer Energie an der f reien Oberflache 
flussiger Korper, von W. Spring, Zeit. physik. Chem., 4. 658-662, (1889). 



68 THE SOIL SOLUTION 

by Liebreich, Becquerel, Lieving and other investigators. So- 
called "contact reactions," as in the production of sulphuric acid, 
are now familiar processes finding commercial applications. And 
the solubility of some substances at least, notably gypsum, has 
been shown to vary considerably with the size and consequent 
shape of the particles in the solid substance in contact with its 
solution.^ 

It has been shown that some soils will at times produce the 
blue coloration in alcoholic solutions of guiac, which is char- 
acteristic of oxidases, and yellow aloin solutions are sometimes 
colored red. Hydrogen peroxide is decomposed by some soils 
even after they have been thoroughly ignited to get rid of all 
organic imatter. But in how far these efifects may be due to 
surface influences can not be positively stated ; yet uncompleted 
investigations by Dr. M. X. Sullivan indicate that some of these 
phenomena at least must be attributed to specific influences (al- 
though probably of catalytic character) of particular soil com- 
ponents, such possibly as manganous oxide or ferric oxide ; but 
the mechanism of the reactions is as yet largely speculative. 

The soil is composed in large part of very fine particles of 
rounded shape, exposing relatively an enormous surface to the 
soil solution, and normally this solution is mainly under capillary 
conditions, so that we should expect that many reactions would 
take place quite differently in the soil from the way they would 
in a beaker or flask. This fact has been generally overlooked 
or ignored, and is probably the explanation of many of the ap- 
parently anomalous results hitherto reported in chemical in- 
vestigations of soils. Abnormal solubilities, precipitations, oxi- 
dations or reductions are frequently found in the literature, and 
when their abnormality is noted at all, they are too often and 
w'ith slight show of reason ascribed to indefinite bacterial action 
or more mysterious vital agencies. Many of them are undoubt- 
edly the results of surface actions. Unfortunately, aside from 
^ See especially, Beziehungen zwischen Oberflachenspannung und 
Loslichkeit, von G. A. Hulett, Zeit. Phys. Chem.. 37 3S5-406, (1901). 
Loslichkeit und Loslichkeits Beeinflussnng, von V. Rothmund, p. 109, 
(1907) ; Principles theoretiques dcs mcthodes d'analyse minerale, par G. 
Chesneau, p. 16-25, (190O). 



ABSORPTION BY SOII,S 69 

some few studies of absorption phenomena, surface effects have 
received httle or no attention from soil investigators, ahhough 
obviously one of the most important and apparently fruitful 
fields, requiring immediate attention. Enough is known to justi- 
fy the statement that the chemistry of the soil need not be, and 
probably is not, the chemistry of the beaker. 



Chapter IX. 

THE RELATION OF PLANT GROWTH TO CONCENTRATION. 

That the concentration of the mineral constituents in the soil 
sohition under normal conditions is competent for plant support, 
is shown by numerous experiments. Birner and Lucanus^ in an 
experiment that has long since become classic, found that they 
could raise wheat to maturity in a well-water, the concentration 
of which was approximately i8 parts per million with respect 
to potassium, and 2 parts per million with respect to phosphoric 
acid, while the corresponding concentrations of the soil solu- 
tion are normally about 25-30 parts per million of potassium 
and 6-8 parts per million of phosphoric acid. Nevertheless 
Birner and Lucanus report that the wheat grown in the well- 
water throve even better than that grown at the same time in a 
rich garden mold. Since then many investigators in numerous 
trials have obtained similar results. Recently wheat, corn, and 
some of the common grasses have been grown to a satisfactory 
maturity in tap water with a concentration of about 7 parts per 
million of potassium and 0.5 parts per million of phosphoric acid. 
And repeatedly wheat plants, grasses, cowpeas, vetches, potatoes 
and other plants have grown in a satisfactory way in solutions 
made by shaking up a soil in distilled water and separating from 
the solid particles by means of filters of unglazed porcelain. 

There can be no doubt, therefore, that the soil solution is 
normally of a concentration amply sufficient to support ordinary 
crop plants, and is maintained at a sufficient concentration, so 
far as mineral plant nutrients are concerned. Undoubtedly, how- 
ever, variations in the concentration of the soil solution can, 
and often do, take place, and the results of laboratory experi- 
ment indicate that they probably produce effects on plants. 

It has been shown in water-culture experiments wath wheat, 
that if a given ratio of mineral nutrients be maintained, relatively 
small effect is produced on the growing plants by varying the 

' Wasserculturversuche mit Hafer, von Dr. Birner und Dr. Lucanus, 
Landw. Vers.-Sta., 8, 128-177, (1866). 



REI.ATION OF PLANT GROWTH TO CONCENTRATION 7 1 

concentration over a wide range, in one case from 75 parts per 
million to 750 parts per million/ and this effect seems to be large- 
ly independent of the nature of the particular mixture of solutes. 
But varying the relative proportions of the mineral constituents 
has been shown by numerous experiments to produce very 
marked changes in the growth of plants. Not only does a con- 
trol of the concentration and proportion of the mineral con- 
stituents of a solution produce a more rapid, or a slower growth, 
a greater or lesser total growth, but it produces differences in 
the character of growth ; as for instance, causing the tops to 
grow relatively faster than the roots, or vice versa. However, 
many effects of this type can be produced, and sometimes more 
readily, by soluble organic substances, or mechanical agencies. 
The mechanism of these effects is by no means clear, in many 
cases. That other causes obtain than a sufficient supply of 
mineral nutrients will be shown in the following chapters. Ex- 
periments with wheat seedlings in water cultures, where the 
weights of the green tops were taken as the measure of growth, 
showed that the most favorable ratio was one of phosphoric 
acid (PO4) to three or four of potassium (K), about the ratio 
which has been found to exist normally in the soil solution of 
humid areas of the United States, namely, 6-8 parts per million 
of phosphoric acid to 25-30 parts per million of potassium. 

All growing plants require for their growth and development 
various organic compounds containing carbon, hydrogen, oxy- 
gen and nitrogen. The higher crop plants with which agri- 
cultural investigations appear to be more immediately concerned, 
seem to have inherent power to produce these needed substances 
within themselves. But it is becoming more and more evident 
that the large problem of soil fertility, or the relation of the 
soil to crop production, frequently if not generally involves the 
growth and development of lower organisms including ferments 
and bacteria. These may or may not in particular cases, favor 
the growth of the desired higher plants. Many of these lower 
organisms require certain organic compounds or thrive better 

^Effect of the concentration of the nutrient solution upon wheat 
cultures, by J. F. Breazeale, Science, n. s., 22, 146-149, (1905). 



JZ THE soil. SOLUTION 

if these are brought to them in the soil solution, and indeed 
evidence is not lacking that such may sometimes be the case 
even with the higher plants. Certainly their growth can be 
much attected by the presence of different organic substances in 
the nutrient solution. Enough work has been done in this field 
of investigation to show that the concentration of the soil so- 
lution or artificial nutrient solution with respect to the organic 
compounds must generally be low ; too high a concentration al- 
ways inhibits growth or even produces death ; and there is prob- 
ably an optimum concentration, or one at which the plant will 
grow best ; but this optimum concentration varies with the specif- 
ic nature of the plant, the presence of other dissolved substances, 
mineral or organic, and possibly with other factors. While a 
notable amount of work has thus been done in a field of inquiry 
obviously of practical as well as theoretical interest, almost no 
definite information has as yet been obtained as to the concen- 
tration of organic substances in the soil solution, or its effect 
upon plants under field conditions, excepting in the case of the 
nitrates, the products of bacterial activities. The concentration 
with respect to nitrates is known to vary greatly from a few 
parts to several thousand parts per million, and this sometimes 
within a few days or even hours. The great changes in con- 
centration with respect to nitrates, the rapidity of the changes, 
and the correspondingly large effects on growing plants make 
this a subject requiring special treatment by itself. This at 
present seems more easily appreciated from a consideration of 
the bacteria involved, and will not be discussed more fully here.^ 
Of the ash constituents of plants, there must be in the soil 
solution, potassium, magnesium, phosphorus, sulphur and iron 
for any plant growth, and for the higher crop plants, calcium 
' See : The fixation of atmospheric nitrogen by bacteria, by J. G. 
Lipman, Bull. No. 8i, Bureau of Chemistry, U. S. Dept. of Agriculture, 
1904 ; A review of investigations in soil bacteriology, by Edward B. 
Voorhees and Jacob G. Lipman, Bull. No. i94> Office of Experiment Sta- 
tions, U. S. Dept. of Agriculture, 1907 ; The physiology of plants, by 
W. Pfeffer, translated by A. J. Ewart, vol. i, p. 388 et seq., 1900; The 
effect of partial sterilization of soil on the production of plant food, by 
Edward John Russell and Henry Brougham Hutchinson, Jour. Agric. 
Sci., 3, ni-144, (1909)- 



RELATION OJ? PLANT GROWTH TO CONCENTRATION "JT, 

must also be present. Of these, iron is usually present in barely 
appreciable concentration and more than this is not desirable, 
or is even harmful for common crop plants. Under the normal 
conditions for soils in humid areas, sulphur also is usually pres- 
ent in scarcely more than appreciable quantities and there is 
no positive evidence to show that higher concentrations are es- 
pecially desirable, though this may be the case for certain crops, 
such for instance as the onion. Phosphorus is usually present 
to the extent of 5 or 6 parts per million of phosphoric acid 
(P2O5), while it has repeatedly been shown that such crops as 
wheat can thrive and make a good growth with a concentration 
a tenth of this. It appears to be clear therefore that as far as 
food supply is concerned there is normally an ample supply of 
phosphorus in the soil solution ; but it does not follow that in- 
creasing the concentration of the solution if only temporarily 
would riot result in favorable effects upon growing plants. 

A consideration of the bases, however, introduces serious diffi- 
culties, which will probably rec|uire much further research by 
the plant physiologist as well as the soil chemist. It is impossible 
as yet to determine the concentrations at which different plants 
will not grow. It is even impossible to determine the concentra- 
tions at wdiich they will thrive best. It seems certain that 
different crop plants require different amounts of these minerals, 
but W'hether or not they require different concentrations of the 
constituents in the nutrient solution for their several best growths 
is yet not clearly showm. It now seems probable that to some 
extent at least these basic mineral nutrients can replace one 
another for the plant's metabolism. It has been show-n in the 
case of certain lower plant organisms that potassium can be 
more or less successfully replaced by rubidium and caesium, and 
in the case of some higher plants, possibly calcium, magnesium 
and potassium can partially replace one another.^ In spite of 
the fact that sodium as well as potassium is a necessary constit- 
uent for the metabolism of higher animals which feed upon 

"^ For a more detailed discussion of this subject, and the functions 
of the several ash constituents in plant nutrition, see : The physiology 
of plants, by \V. Pfeffer. translated by A. J. Ewart, vol. i, p. 410, ct seq., 
1900. 



74 THE SOIL SOLUTION 

plants, it is generally held that sodium can not replace potassium 
in the processes of plant growth, although Wheeler and his 
colleagues have advanced evidence to show that a partial re- 
placement is possible.^ It seems evident, however, that no gen- 
eralizations can hold concerning the effect of the concentration 
of any one base on plant growth which do not include recogni- 
tion of possible modifications due to the presence of other bases; 
and the formulation of such generalizations must needs wait 
upon a more thorough knowledge of the parts played by the 
several mineral nutrients in the metabolism of different classes 
of plants. 

As to forms or chemical combinations in which the inorganic 
constituents of the soil solution are best adapted to plant growth, 
but little can yet be said other than that the diff'erent combina- 
tions do have an importance. Some empirical information is 
available, such as for instance, that potassium sulphate or car- 
bonate is a better fertilizer for some crops than is potassium 
chloride. It is known that the mineral nutrients in the plant are 
partly in inorganic combinations but largely in organic combi- 
nations. But the causal relationships are yet to be worked out. 
And finally, although some meagre experimental data have been 
obtained as to the effect of certain inorganic constituents on the 
absorption of others, by particular plants, the mechanism of 
absorption itself, including the selective powers of the plant, is 
yet wanting an adequate explanation. 

^ The effect of the addition of sodium to deficient amounts of po- 
tassium, upon the growth of plants in both water and sand culture, 
by B. L. Hartwell, H. J. Wheeler and F. R. Pember, Report Rhode 
Island Agricultural Experiment Station, 1906-7, p. 299-357. 



Chapter X. 

THE BALANCE BETWEEN SUPPLY AND REMOVAL OF 
MINERAL PLANT NUTRIENTS. 

The mechanism of the solution and transport of mineral nu- 
trients developed in the preceding pages makes it of interest to 
determine the relation between the possible or probable supply 
of mineral plant nutrients and crop demands over large areas. 
The inquiry can be formulated more specifically: Is the move- 
ment of mineral plant nutrients towards the surface soil equal to 
or in excess of the removal by drainage waters and garnered 
crops? Satisfactory data are yet wanting for anything like 
exact computations, but approximate figures are available which 
appear sufficient for the present purpose. 

The rainfall (R) can be considered as disposed in three por- 
tions, the fly-off (/), the run-ofif (r), and the cut-off (c). Stat- 
ing this as an equation, 

R = f -{- r + c. 
The cut-off can be resolved into the portion (a) seeping through 
the soil to ultimately join the run-off, and the portion (b) re- 
turning to the surface to ultimately join the fly-oft'. Stated as 
equations, 

R = fJ^r-\-a-\-b 
= f-\-b-{-(r + a). 
In other words, the rainfall can also be considered as made up 
of the fly-off, the capillary water of the soil and the drainage 
from the area. According to Murray,^ Geikie,- Newell,^ and 
others, the drainage water for humid areas, or such an area as 
the United States as a whole, would be between 20 and 30 per 
cent, of the rainfall, the major portion coming from seepage 
water rather than surface drainage. Assuming the higher fig- 

^ On the total annual rainfall on the land of the globe, and the re- 
lation of rainfall to the annual discharge of rivers, by Sir John Murray, 
Scot. Geog. Mag., 3, 65-77, (1887). 

' Textbook of Geology, by Sir Archibald Geikie, p. 484, (1903). 

^ In Principles and conditions of the movements of ground water, by 
F. H. King, Ann. rept. U. S. Geol. Surv., 19, II, 59-294, (1897-98). 



'jd the: soil solution 

ure, and making the further very probable assumption that the 
capillary water in the soil {h') is never less than the fly-off or 
the water that evaporates during rain (/), it follows from tlie 
equations given that the capillary water is at least 35 per cent, 
of the rainfall. If we assume the lower value for the drainage, 
then the capillary water is at least 40 per cent, of the rainfall, 
and if we assume the extreme case — that the fly-oft' is practically 
negligible — the capillary water becomes 80 per cent, of the rain- 
fall. It appears, therefore, that in all probability the proportion 
of the cut-off water which returns to the surface as film water 
or capillary water is always greater, and generally much greater, 
than the portion which seeps through the soil to join the run- 
off. 

From the available data, it appears that the average concen- 
tration of the run-off waters of the United States is about 1.8 
parts per million of potassium (K) and about 0.6 parts per mil- 
lion of phosphoric acid (P04),^ while the concentration of the 
capillary groundwater is some ten or twelve times greater. But 
even if these concentrations were the same, it is altogether prob- 
able that very much the greater part of the mineral plant nu- 
trients dissolved by meteoric waters is continually, if slowly, 
moving towards the surface of the soil. 

The average rainfall of the United States may be taken as ap- 
proximately 30 inches.-" If it be assumed that the discharge 
into the sea is 25 per cent., then the capillary cut-oft' water is 
at least 37.5, and probably nearer 70 per cent, of the rainfall. 
King's experimental work-^ indicates that the higher figure is 
much nearer the truth. Computing from the concentrations 
just cited, with the equations given above, it is found that ap- 
proximately 3,500,000 tons of potassium (K) and 1,200,000 tons 

' Estimated from data in Bull. No. 330, U. S. Geological Survey, 
The data of geochemistry, by Frank Wigglesworth Clarke, 1908, p. 53-90. 

" The latest authoritative statement is that the average annual rain- 
fall of the United States is 29.4 inches ; see : Water Resources, by W J 
McGee, vol. i, p. 39-49, and Distribution of rainfall, by Henry Gannett, 
vol. 2, p. 10-12, Report of the National conservation commission, Senate 
doc. No. 676. 6oth Congress, 2d session, 1909. 

'King: loc. cit., p. 85. 



MINERAIv PLANT NUTRIENTS TJ 

of phosphoric acid (PO4) are carried into the sea annually from 
the United States, while from 48,000,000 to 100,000,000 tons 
of potassium and 18,000,000 to 40,000,000 tons of phosphoric 
acid are being carried towards the surface of the soil. If it be 
assumed that an average of one ton per acre of dry crop con- 
taining one per cent, potash and 0.6 per cent, phosphoric acid^ 
be removed from the entire area of the United States, then the 
annual loss from this source would be 24,000,000 tons of po- 
tassium and 14,000,000 tons of phosphoric acid. Consequently, 
there is an ample margin between the losses by cropping and 
seepage waters, and the supply of capillary waters. It is true 
that cases exist where the production of vegetable matter is much 
greater than a ton to the acre, productions of five tons or even 
more being on record. But such cases occur only where the 
water supply is also greater, either through natural rainfall or 
artificial irrigation ; and it should also be borne in mind that the 
production of so large a mass of green crop involves a consid- 
erable drawing power on the water in the soil in addition to the 
evaporation which would take place at the surface under ordi- 
nary conditions. In other words, the plant would then be play- 
ing no small part in drawing to itself its needed supplies of water 
and dissolved mineral nutrients. 

The question may be asked, if the processes outlined above 
are generally operative, why accumulations of soluble mineral 
substances are not usually found at the surface of the soil. As 
a matter of fact such accumulations do occur normally when the 
evaporation at the surface is relatively large, that is, under arid 
conditions. And under humid conditions it appears to be a gen- 
eral rule that the surface soil contains more readily soluble or 
absorbed mineral matter than do sub-soils.- No great accumula- 

' Estimated from Wolff's tables, How crops grow, by Samuel W. 
Johnson. i8qo, appendix. 

' See, for instance : Investigations in soil management, by F. H. 
King, Madison, Wis., 1904, p. 62 ct scq. This tendency towards a higher 
content of absorbed soluble mineral matter in the surface soil has been 
amply confirmed by other experiments. It has been advanced as an 
argument against the assumption that the hydrolysis of the soil minerals 
is a reversible process. But as pointed out elsewhere in the text, many 
of the soil minerals can be made in the wet way at more or less elevated 
temperatures and the more rational explanation is simply that at ordi- 
nary temperatures the rate of formation is exceedingly slow. 



78 THE SOIL SOLUTION 

tion occurs at the surface normally under humid conditions be- 
cause the rainfall is sufficiently distributed throughout the year 
to enable the cut-off water to carry back promptly into the lower 
soil levels any excessive amount of soluble material, there to 
start anew its slower ascent towards the surface. 

Calculations such as those here presented are at the best open 
to many objections, and it is wise to avoid giving them too much 
emphasis. So far as the available data justify any conclusion, 
however, it appears that the rise of capillary water is entirely 
capable of maintaining a sufficient supply of mineral nutrients for 
crop requirements ; and furthermore, it is obvious that the prob- 
lem of the supply of mineral plant nutrients is dynamic and can- 
not be successfully attacked by considerations which are essen- 
tially static. 



Chapter XI. 

THE ORGANIC CONSTITUENTS OF THE SOIL SOLUTION. 

The organic substances in the soil are tissue remains, to a large 
extent of plants, and to a less extent of animals; and it is to be 
expected that there may be found also in the soil the substances 
which were in the organisms at the time of their death, and de- 
gradation and decomposition products derived from these. More- 
over, there are to be anticipated numerous products of bacterial 
origin, secretions of algae, fungi, etc., so that the organic com- 
plex in the soil may contain numerous substances of widely 
different chemical characteristics. Degradation products of pro- 
teins, fats, and carbohydrates, as well as decomposition products 
may be expected in almost any soil. But it does not follow that 
any particular organic substance (excluding, of course, carbon 
dioxide or nitrates) is to be found in every soil. No general- 
ization regarding the organic substances in the soil can be made 
such as that formulated for the inorganic compounds. It is 
probable that further investigation will show certain organic 
substances or classes of substances to be common to most soils, 
but it is reasonably certain that many other organic substances 
will be found in only a few soils, or occasionally, and these latter 
will be often a prominent factor characterizing the particular 
soil in which they may occur. 

Although no broad generalization is justified regarding the 
composition of the soil solution with respect to organic sub- 
stances dissolved, nevertheless the extension of the methods 
developed in the study of the inorganic substances dissolved has 
led to a considerable knowledge of the organic ones. 

In view of the facts shown in the preceding chapters, and 
at the same time recognizing that good and poor soils respec- 
tively must show differences in the soil solution if the funda- 
mental thesis is valid as to the relation of soils to crop produc- 
tion, experiments have been made to investigate in a comparative 
way solutions obtained from good and poor soils of the same 
type, locality, and physical characteristics. For this purpose 
two samples of soil were taken from adjacent fields which had 



80 THE SOIL SOLUTION 

been under observation for two years. The soils were of the same 
type, Cecil clay, and were so similar in their physical charac- 
teristics as to be distinguished with difficulty in the laboratory. 
On one field a good crop of wheat was grown, followed by a 
good crop of clover and tame grasses. On the other field, the 
corresponding crops had been quite poor. The field yielding 
the good crops had been plowed somewhat deeper, and had 
previously received a moderate application of stable manure. 
Otherwise, so far as could be learned, the cultural history of the 
fields had been the same. For convenience, the sample from 
the first field will be designated "good," and from the other 
"poor." 

Aqueous extracts from these soils were prepared, the same 
proportion of distilled water to soil being taken in each case, 
and the time of contact being the same. The solutions were 
freed from suspended matter by being passed through Pasteur- 
Chambcrland bougies under pressure. Young wheat seedlings 
germinated at the same time, and selected carefullv for uni- 
formity of size and apparent vigor, were grown in these solu- 
tions for three days. At the expiration of this period the seed- 
lings in the extract from the good soil were about five inches in 
height, and the roots were clear, clean and turgid. The plants 
in the poor extract were scarcely three inches in height, and the 
roots were assuming a slimy, unhealthy appearance and becom- 
ing flaccid at the tips. The plants were then all removed, the 
roots washed carefully in tap water ; the plants which had been 
in the poor solution were placed in the good solution, and those 
whicli had been in the good solution were placed in the poor solu- 
tion. At the end of four days further, the poor plants had surpassed 
in height the ones which had previously been in the good solu- 
tion, and the roots had acquired the general characteristics of 
healthy plants. These which had been originally in the good 
solution and then transferred to the poor, had made little addi- 
tional growth, and the roots had become somewhat flaccid.^ 

This experiment was repeated several times, not only with 
The success of this and of many of the following experiments 
was due in large measure to the skill and patience of Mr. James E. 
Breazeale. 



ORGANIC CONSTITUENTS OF THE SOIE SOLUTION 8 1 

the soils cited but with samples from adjacent good and poor 
spots in fields on several soil types from widely separated areas ; 
for instance, Cecil clay from near Statesville, North Carolina; 
Sassafras loam from Maryland ; Windsor sand from Delaware ; 
and similar results were obtained. In other words, these water 
cultures produced plants which showed much the same differ- 
ences, in kind and degree, as had been observed in the field. 
This was recognized as an important step forward, for it indi- 
cated that zifhatcver zvas making a difference in the crop-produc- 
ing pozver of these soils in the field zvas transmitted to their 
aqueous extracts, and methods for studying the chemical prop- 
erties of solutions are far in advance of methods for studying 
mixtures of solids. 

The soil extracts described above were subjected to a careful 
analysis for their mineral constituents. They were found to be 
practically identical in this respect. Further, the poor extract 
contained decidedly more nitrates than the good — from three 
to four times as much. It follows, therefore, that the difference 
in the soils which produced a good and a poor crop respectively, 
was not due to a difference in mineral plant nutrients, or other 
mineral differences probably, nor to their respective content of 
nitrates. Consequently, the poor solution was such, not because 
of the lack of anything, but because of the presence of some- 
thing inimical or "toxic" to plant growth ; and further, this 
something must be an organic substance or substances more or 
less soluble in water. This conclusion was confirmed in the 
following way. 

Samples of the poor solution from the soil obtained near 
Statesville, N. C, were diluted twice, five times, and ten times, 
and wheat seedlings were grown in these solutions, using a sam- 
ple of the good solution as a check. It was found after several 
days growth that the plants in the solution diluted tenfold were 
about as good, or perhaps slightly better, than those grown in 
the check solution. In every case diluting the poor solution 
had improved it for plant growth, and the higher the dilution 
the greater the improvement, in spite of the consequent dilution 
of the mineral plant nutrients. The only explanation of these 



82 THE SOIL SOLUTION 

results whicli has yet suggested itself is that the toxic organic 
substances present were less effeciive on dilution until the con- 
centration reached a point where they actually became stimula- 
tive, as is common with toxins of every character. 

Another set of experiments confirmed the conclusion that the 
poor solution contained some organic substance inhibitory to 
plant growth. A number of water cultures was prepared from 
the aqueous extract of the poor soil, and lime in various forms 
was added to the cultures. To two of the cultures lime car- 
bonate and lime sulphate respectively were added in excess, so 
that there was in each case a powdered solid at the bottom of 
the containing vessel. At the end of two days the wheat seed- 
lings which were growing in the vessels containing the pow- 
dered solids bad decidedly outstripped those growing in all the 
others, the tops having the appearance of unusually good and 
healthy plants. The roots were of a very remarkable character, 
being exceptionally long, very turgid, clear, clean and translu- 
cent. 

At once, new experiments were carried out in which there 
were added to the poor solution, precipitated ferric hydroxide 
freed from all adhering salts, precipitated alumina, shredded 
filter-paper, absorbent cotton, or carbon black. In every case the 
same result was obtained as before, a much improved growth 
of top and a vastly better root development. Since, by no 
possibility could these various added substances have increased 
the concentration with respect to mineral nutrients, another ex- 
planation must be sought. Aside from their insolubility, the 
one property common to these various substances was the large 
amount of surface they brought into contact with the solution. 
The one obvious explanation of their effects on the growth of 
the wheat seedlings, therefore, is that they withdrew or ab- 
sorbed from the solution some substance or substances deleteri- 
ous to plant growth. As diluting with respect to mineral nutri- 
ents could not possibly be expected to improve the cultural value 
of the solution, the conclusion seems evident that the effect pro- 
duced by these various absorbents was due to more or less com- 
plete removal from the solution of organic substances inhibitory 



ORGANIC CONSTITUENTS OF THE SOIE SOLUTION 83 

to plant growth. These experiments were then repeated in 
a modified form by shaking- the poor solution with such ab- 
sorbents as precipitated ferric oxide or carbon black and filtering 
before adding the seedling plants. The solutions thus pre- 
pared proved very satisfactory nutrient media, although the de- 
cided elongation of the roots, always observed when the ab- 
sorbents were in contact with the solutions, was not so notice- 
able with these filtered solutions. 

The experiments just described were repeated with extracts 
from a number of soils which were supporting or had recently 
supported poor crops. The accumulated mass of evidence ad- 
mits of no doubt that in many cases the apparent lack of fertility 
of a soil is due to the presence of some organic substance or 
substances soluble in soil water. This point established, there 
was studied the effect of fertilizers when added to aqueous ex- 
tracts from poor soils. 

A large amount of experimenting has been done on this sub- 
ject. It has been found that the common commercial fertilizers, 
as well as many other substances, when added to the soil ex- 
tract containing growing plants, sometimes improve the plants, 
sometimes the contrary. But, in general, those particular sub- 
stances which improve any given soil for a crop also improve the 
aqueous extract of the soil for the growth of the same crop plant ; 
i. c., should a soil be known to respond well to the application of 
superphosphates when planted to wheat, then the probability is 
great that the aqueous extract of the soil will be improved as a 
culture medium for the wheat plant by addition of calcium 
phosphate. Particularly important in this connection are cer- 
tain experiments with organic fertilizers. 

A soil which had been found to be quite unproductive with 
regard to wheat and ordinary tame grasses yielded, however, 
a much better growth of plants if pyrogallol or better pyrogallol 
and lime were added to the soil some days before planting. An 
aqueous extract of this soil tested with young wheat seedlings 
produced but a poor growth, as did the soil itself. But with 
the addition of pyrogallol or pyrogallol and lime to the soil ex- 



84 THE soil. SOLUTION 

tract, and especially if the extract so treated were allowed to 
stand for a few days with free access of air, there was obtained 
a culture medium which yielded remarkably good results with 
wheat seedlings. Not only was there an excellent and increased 
development of tops, but the roots of the seedlings grown in the 
solution treated with pyrogallol were unusually long, turgid, 
clear and translucent. Here, then, there was obtained an in- 
creased amount and improved character of growth by the addi- 
tion of a substance which contained only carbon, hydrogen and 
oxygen, and no recognized plant food. Other organic sul> 
stances, such for instance as tannin, gave similar results. 

With the recognition that the presence of organic dissolved 
substances in the nutrient medium produced effects on a grow- 
ing plant of as great or even greater magnitude than those pro- 
duced by inorganic dissolved substances, there was carried out a 
number of experiments to test more specifically such substances 
as might reasonably be expected to be present naturally in soils. 
The results thus obtained suggested experiments with other re- 
lated substances. The first substance to suggest itself is stable 
manure. Taking it all in all. this substance is probably the most 
efficient as well as the most generally used soil amendment in 
the experience of mankind. The good effects produced by this 
substance have in the past been generally considered as due to 
the readily "available" potash, phosphoric acid and nitrogen it 
contains, but thoughtful experimenters and agriculturists have 
long doubted that this explanation is sufficient, since, after all, 
the mineral constituents of stable manure are usually small in 
amount, and out of all proportion to the eft'ects resulting from 
its use. That some of the results are due to an improvement in 
the physical condition of the soil when manure is used has quite 
rightly been generally assumed ; but to its content of nitrogenous 
components its value has in the main been ascribed. 

A well-fermented aqueous extract of stable manure was pre- 
pared, and filtered free of suspended solids. Four equal vol- 
umes of this solution were taken. Three of these portions were 
evaporated to dryness in platinum dishes, and the residues 



ORGANIC constitue;nts of the; soii^ solution 85 

incinerated.. To the dishes containing the ash were added re- 
spectively nitric acid, sulphuric acid, and hydrochloric acid in 
slig-ht excess, and the dishes again brought to dryness. Water 
cultures for wheat seedlings were then prepared.^ Into one was 
introduced the given volume of manure extract ; into another the 
SLsh from an equal volume of the extract which had subsequently 
been treated with nitric acid ; and cultures with the ash which 
had been treated respectively with sulphuric and hydrochloric 
acid were similarly prepared. After ten days growth, the plants 
from the several cultures were compared. The plants from the 
cultures which contained the sulphates and the chlorides were 
not materially different from the plants grown in the check 
culture. The plants from the nitrate culture had larger shoots, 
but shorter roots than the check plants. But the plants grown 
in the culture to which the manure extract had been added direct- 
ly had by far larger and better shoots and the roots were incom- 
parably superior to those grown in any other culture, being 
larger, thicker, better branched, clear, bright and translucent, and 
very turgid, very like the roots obtained in cultures to which car- 
bon black or precipitated ferric oxide had been added. 

The results of this experiment, which has been repeated a 
number of times, using manure extracts of various origins, leave 
no doubt that it is the organic components of the manure which 
produce the characteristic effects, for the ash culture contained 
all and even more of the mineral constituents "available" in the 
original extract, and the nitrate culture excluded any explana- 
tion based on the nitrogenous content of the manure. This con- 
clusion was supported by the results of another experiment. 

To a manure extract was added alcohol, which precipitated 
most of the organic dissolved substances but very little of the 
inorganic ones. The precipitated organic matter was filtered 
off, dried carefully in a water oven to eliminate the alcohol, and 
then taken up in sufficient water to equal the original volume 
of manure extract. The filtrate containing the major part of the 

' Further studies on the properties of unproductive soils, B. E. Liv- 
ingston et ai, Bull. 36, 1907, and 48, 1908, Bureau of Soils, U. S. Dept. 
Agriculture. 



86 the; soil, solution 

salts was boiled vigorously to eliminate the alcohol and water 
was then added to restore the original concentration. A third 
solution was prepared by bringing together the organic and in- 
organic substances which had previously been separated as above 
described. The three solutions were used as water cultures for 
wheat seedlings, a solution of the original manure extract being 
taken for a check culture. The original manure extract and the 
reconstructed manure extract gave plants of about equal de- 
velopment. The culture containing the organic dissolved sub- 
stances only, gave plants of nearly, but not quite, equal de- 
velopment to those grown in the check culture. But the plants 
grown in the solution containing the dissolved minerals only, 
while fine plants and making what would ordinarily be considered 
a good development, were decidedly smaller as regards their 
aerial parts, and the roots were in no wise comparable to the 
roots of the plants grown in the cultures containing the dissolved 
organic substances. 

This last experiment has been repeated, with dissolved sub- 
stances prepared from another manure extract, but in this case 
the organic and inorganic substances were separated by dialysis. 
This suggested yet another experiment, in which it was sought 
to hasten the process of dialysis, by introducing electrodes into 
the mianure extract, each electrode being surrounded by some 
porous membrane, either of parchment paper, or unglazed por- 
celain. Not only were the mineral constituents of the manure 
extract readily separated in this way, passing into the electrode 
chambers, as did also to some slight extent organic compounds, 
but also about the outer walls of the electrode chambers there 
was marked segregation and deposition of organic materials. 
The organic substances deposited at the cathode were found to 
stimulate greatly the growth of wheat seedlings while those de- 
posited at the anode were found to retard the growth of seed- 
lings. It seems probable, therefore, that stable manure con- 
tains organic components which produce as great or greater 
effects upon growing plants as do the inorganic substances it 
contains : that on the whole these organic components induce 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 87 

increased plant growth, but some of them, by themselves alone, 
would retard plant growth. 

In a similar way green manures have been examined. If 
fresh clover, alfalfa, or cowpeas, be macerated and an aqueous 
extract thus prepared, it will in general be quite toxic to plants 
such as wheat; and if this extract be allowed to stand and fer- 
ment or sour the resulting solution will be totally unfit for the 
growth of seedling plants. But if the clover, alfalfa, or cow- 
pea vines be allowed to wilt thoroughly before being macerated 
and extracted, or if they be macerated and incorporated with 
soil and allowed to remain thus for ten days or a fortnight be- 
fore being extracted ; then, the resulting solution will be quite 
stimulating to such plants as wheat, corn or the grasses, when 
added either to water or soil cultures. It would seem, therefore, 
that the mineral constituents of the legumes commonly employed 
as green manures are less important than the organic, in affect- 
ing the growth of crops subsequently planted, and the inhibitory 
or toxic action of fresh green manure seems to be recognized in 
the common practice of waiting some days after turning under 
a green manure crop before seeding to a new crop. 

The wilting of a green manure involves a darkening and some 
blackening of the mass, with apparently some absorption of 
oxygen. This fact has suggested a trial of other organic sub- 
stances which show a decided ability to absorb oxygen. Among 
such substances, pyrogallol stands preeminent. It has been 
shown that when pyrogallol, or better pyrogallol and lime, is 
added to certain soils, naturally low in productive power, and 
allowed to stand for a few days, these soils are readily brought 
into good condition and support good crops of wheat, rye, or 
grasses. Pyrogallol in water cultures is rather toxic to wheat 
plants, even in quite dilute solutions. But if the aqueous solu- 
tion of pyrogallol be allowed to stand exposed to the air, and 
better if the solution be made slightly alkaline as by the addi- 
tion of lime, oxygen is absorbed, and a dark brown or blackened 
solution is soon formed, which is stimulating to wheat seedlings. 
Many experiments have indicated it to be a general rule that 



88 THE soil, SOLUTION 

soluble organic substances wbich are toxic to plant growth yield 
oxidation products which are harmless or positively beneficial. 

The suggestion has been made that th.e well-known infertility 
of subsoils, when freshly turned up, is caused by the presence 
of alkaloids of the purine or codeine type, due to the activities 
of anaerobic bacteria. Water cultures and pot cultures show 
that while these substances do have a marked effect on plant 
growth, it is, frequently, quite beneficial ; strychnine for example, 
in certain concentrations, produces a very decided stimulation in 
the growth of wheat seedlings. It is clear that some other ex- 
planation wall have to be sought for the lack of fertility of sub- 
soils. 

A number of the substances which may be expected for one 
reason or another to be present in soils, have been investigated as 
to their effect on plants. In this connection may be cited the 
work of Livingston^ and of Dachnowski,- who have studied the 
effect on vegetation of the organic substances dissolved in bog 
waters. In the following table are given the results obtained 
by growing wdieat seedlings in solutions containing some one of 
a number of substances which might be expected to occur in a 
soil or to be derivatives of such substances. It will be observed 
that in the case of these dissolved organic substances, as has 
been repeatedly established with the inorganic ones, in concentra- 
tions sufficiently dilute not to be toxic, they generally show 
the opposite effect and appear to be stimulating. 

* Physiological Properties of Bog Water, by B. E. Livingston, Bot. 
gaz., 39, 348-355, (1905)- 

"The toxic property of bog water and l)0g soil, l)y Ah'red Dachnow- 
ski, Bot. gaz., 46, 130-143, (1908). 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 



89 



H 








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55 




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THE SOIL SOLUTION 



















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ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 



91 



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THE SOIL SOLUTION 







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ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 



93 



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94 THE SOIL SOLUTION 

a. Aspartic acid has been found in young sugar-cane and in seedling-; 
of the bean and pumpkin. 

b. Asparagine was first found in asparagus ; but has since been 
shown to be relatively abundant in many species. 

c. GlycocoU is one of the simpler and more common degradation 
products of proteins. 

d. Alanine is a common degradation product of proteins and is 
related chemically to phenylalanine, and to tyrosine, which has been 
found in many plants. 

e. Leucine, an amino-acid of a paraffine series and a decomposition 
product of proteids, has been found in certain mushrooms, vetches, 
lupine, gourds, potatoes, corn, etc. 

/. Tyrosine is an important decomposition product of proteids, is 
widely distributed and found in many plants and fungi. 

g. Choline is a derivative of certain lecithins and is found in many 
seeds and growing plants. 

h. Xeurine is a substance closely related to choline, and probably 
formed from it. 

i. Betaine is closely related to both choline and neurine, and is found 
in many seeds and plants. 

./. Alloxan is closely related chemically to convicine, which latter 
is found in beets and certain beans. 

k. Guanine is a widely distributed nitrogenous body, and has been 
found in the seeds of vetch, alfalfa, clover, gourds, barley, sugar- 
beets and sugar-cane. 

/. Xanthine, a substance closely related to guanine, has been found 
in a number of plants. 

ill. Guanidine. a substance chemically related to guanine, has been 
found in a number of plants of different species. 

11. Skatol is a derivative of proteids and is a common product of 
the activities of some varieties of bacteria. 

0. Pyridine has been shown to exist in soils, as such probably, by 
Shorey. who obtained it from certain soils in Hawaii. 

/». Ricin is found in the castor-oil plant. 

q. Mucin has been found in yams. 

r. Pyrocatechin has been found in the bark of various trees, the 
berries of the Virginia creeper, the sap of sugar beets and in several 
varieties of willows. 

J. Arbutin has been found in many plants, especially in some of 
the grasses. 

t. Phloroglucin is easily derived from a number of plant constituents. 

u. Vanillin forms readily from a glucosidc, which is very widely 
distributed in many plants, and by some authorities is supposed to be 
a product of the decomposition of wood tissues. 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 95 

V. Quinic acid, which is found with quinine in the cinchona bark, 
also occurs in beet leaves, certain hays, cranberry leaves, and occasionally 
in other plants. 

w. Quinone has been shown to result from the action of a certain 
fungus, Strcptothrix cltromogeiia, common in soils. 

X. Cinnamic acid is found in certain barks, and forms esters which 
have been found in the leaves of various plants. 

V. Cumarin has been found in a large number of plants, includin;; 
the grasses, beets, sweet clover, etc. 

r. Daphnetin occurs in some species of Daphne and is closely related 
to cumarin. 

aa. Esculin, as well as the corresponding esculetin, has been found 
occasionally in a number of plants. 

bb. Heliotropine, or piperonal, has the odor of heliotrope and is 
found in flowers. 

cc. Borneol occurs in needles of different varieties of pine, fir, spruce 
and hemlock, golden rod and thyme. 

dd. Camphor is closely related chemically to borneol and is secreted 
by a number of plants; it is found in the wood of Cinnainomum, cinna- 
mon root, in the leaves of sassafras, spikenard, rosemary, rosewood, etc. 

ce. Turpentine is a constituent of many plants and coniferous trees. 

Finally, a number of organic substances has been isolated from 
soils. Their composition, and in several cases their constitu- 
tions have been determined. The effects of these on plants, 
when they are present in the cultural media have been studied. 
Thus, Shorey^ was able to isolate picoline carboxylic acid 
(C-H-XO„ ) from certain soils in Hawaii, and this ^ame substance 
has since been found in several soils of the United States. In 
aqueous solutions it is quite toxic to wheat seedlings. Since then a 
number of other definite organic compounds have been isolated 
from soils belonging to at least eight dift'erent classes of organic 
substances, including :- 

Hentriacontane, CgiH,,^. 
. ^lonohydroxystearic acid. CH,(CH,),,CHOH(CH,)oCOOH. 
Dihydroxystearic acid, CH,(CH.),CHOH.CHOH.(CH.), 
COOH. 

Organic nitrogen in Hawaiian soils, by E. G. Shorey, report of 
Hawaii Experiment Station, IQ06, 37-59. 

- Chemical Xature of Soil Organic Matter, bv Oswald Schreiner 
and Edmund C. Shorey, Bull. 74, Bureau of Soils, U. S. Department of 
Agriculture, 1910. 



g6 THE SOIL SOLUTION 

Agroceric acid, C01H42O3. 
Paraffinic acid, C^Ji^gO.^. 
Lignoceric acid, CaiH^sOg. 
Phytosterol, C„6H,,0.H,0. 
Pentosan, C^HgO^. 
Agrosterol, CofiH^.O-HoO. 
Picoline carboxylic acid, C^H-OoN. 
Histidine, CeHgO.Ns. 
Arginine, CgHi^OoN^. 
Cytosine, C.H.ONg.H.O. 
Xanthine, C,H,OoN,. 
Hypoxanthine, C^H^ON^. 
Glycerides, resin acids, etc. 

Some of these, picohne carboxyhc acid, dihydroxystearic acid 
and the pentosan just cited, are toxic to growing plants; others 
are not. The origin and mode of production of these sub- 
stances in the soil is, generally speaking, uncertain and obscure, 
and is yet one of the important fundamental problems confront- 
ing the soil chemist. 

It is important to note that the organic substances thus far 
isolated from soils are of widely varying types, and with very 
different chemical characteristics. As pointed out above, almost 
any type of organic substance is likely to be found in soils, and 
the effects of any of them on growing plants can hardly be pre- 
dicted from a priori considerations. 

It has been found that as a general rule the continued growth 
of one crop in any soil results in a low crop production. Pot 
cultures have given even more pronounced results in the same 
direction. The explanation long accepted is that the soil has, 
as a result of continued cropping, become deficient in some one 
or more of the "available" mineral nutrients. Pot experiments, 
where the garnered crop was returned to the soil and still a 
diminished yield was obtained, throw doubt on this explanation. 
Still further doubt results from water-cultures which, by grow- 
ing a crop in them, become "poor" for subsequent crops, al- 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 97 

though there is maintained in them an ample supply of mineral 
plant nutrients, and they are easily renovated by good absorb- 
ers. These facts find a more satisfactory explanation as being 
due to the production in the nutrient medium of deleterious or- 
ganic substances originating in the growing plant itself. This 
idea seems to have been advanced first by De Candolle, in 1832/ 
to account for the beneficial results obtained by employing a 
rotation of crops. It appears to have been held by Liebig at 
one time, although he subsequently abandoned it in favor of 
the view that the benefits of a crop rotation are due to the sev- 
eral crops requiring different proportions of mineral nutrients, 
and that the disturbance of the balance in the soil produced by 
one crop is not unfavorable to the growth of some other crop. 
Although lacking direct experimental confirmation, this latter 
view of Liebig's has long prevailed among agricultural investi- 
gators, partly by reason of his authority, partly by reason of the 
dominance of the plant-food theory of fertilizers, and partly 
by reason of the fact that the ideas of De Candolle as originally 
advanced included certain errors soon detected. The trend of 
recent investigations has been distinctly in favor of a modified 
form of the view of De Candolle. It has been recognized that 
other factors enter into crop rotations, such as the elimination 
of associated weeds, various kinds of animal, insect and plant 
parasites, preparation of the soil by a deep-rooted crop for a 
shallow-rooted following crop, etc. It has come to be recog- 
nized that there are natural associations of plants, and natural 
rotations of vegetation certainly determined by other than plant- 
food factors. Thus, in the eastern United States, wheat is fol- 
lowed by ragweed naturally, while across the fence cocklebur 
and wild sunflower come in after the corn, the difiference in 
vegetation being as sharply marked after the removal of the 
crops as when they still occupied the land. Analyses of the 
ragweed, for instance, although it is a shallower rooted crop 
than wheat, show that it takes from the soil as much of the 

^ See in this connection, Further studies on the properties of un- 
productive soils, by B. E. Livingston, Bull. Xo. 361 Bureau of soils, Dept. 
of Agric, 1907, p. 7-9. 



98 



Tllli SOIL SOLUTION 



mineral nutrients as does the preceding^ wheat crop. The in- 
vestigation of Lawes and Gilbert- on fairy rings showed that 
the continual widening of the rings can not be satisfactorily 
explained by the comparison of the mineral constituents in the 
soil within and without the rings. Work at Woburn^ on the 
efifect of grass on apple trees finds no other plausible explana- 
tion than that the growing grass produces in the soil organic 
substances detrimental to young apple trees. A number of simi- 
lar cases have been recorded. 

^ Mr. J. G. Smith has made a comparison between the potash nnd 
phosphoric acid content of the wheat and following crop of ragweed 
grown on a farm in Fairfax Co., Va. His unpublished results, with 
som^ others found in the literature, are given in the following; table : 



Material 


Potash 

KoO 

per cent. 


Phosphoric 
acid, P^Oj 
per cent. 


Analyst 


Wheat 


0.76 

1. 78 
1.28 

1. 18 
1.796 

1.79 

I.S09 


0.52 
0.73 
0.35 

0-39 
0.51 

0.41 
0.54 


Smith 




Smith 




Smith 


Ragweed in seed and accom- 


Smith 


Winter wheat in flower. . • . 


Wolff's tables in Johnson's 
"How Crops Grow, "p. 376. 

DeRoode.in Bull. 19, W. Va. 
Agr. Exp. Sta., 1891 

Burney, 2d. Ann. rept. S. 
C. Stat., 1889, p. 146 







On the whole, ragweed seems to require and take from the soil 
about as much mineral matter as does wheat. It is stated by some of 
the dairy farmers near Washington, who cut the mixture of ragweed, 
other weeds and grass following wheat, for a hay crop, that the weight of 
the ragweed crop is generally heavier than that of the wheat crop. 
Therefore the ragweed actually removes more mineral matter from the 
field than does the wheat. These facts lend no support to the popular 
notion that wheat "exhausts" the soil of its "available" mineral plant 
nutrients. For analyses of a number of common .American weeds, see 
.A.nalyses of the ashes of certain w-eeds, by Francis P. Dunnington : Am. 
Chem. Jour., 2, 24-27, (1880). 

^ Note on the occurrence of "fairy rings," by J. H. Gilbert: Jour. 
Linn. Soc, 15. 17-24. (1875)- 

' Second, third and fifth reports of the \\"ol)urn Experimental Fruit 
Farm, 1900, 1903, 1905. 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 99 

Finally, although less work has been done in this direction 
with higher plants than with other organisms, it is now recog- 
nized as a general law of all living organisms that they func- 
tion less readily as the products of their activities accumulate.^ 
These products may, however, be inimical, neutral or even stimu- 
lating to other organisms. 

This problem has been investigated critically by direct ex- 

^ It may not be amiss to point out here that this general law holds 
for all dynamic phenomena. In chemistry, for instance, the general 
law is well recognized that the rate of reaction diminishes with increase 
in the active mass of the reaction products. It can be shown that the 
principle applies to plant growth. Young plants will withdraw potassium 
more rapidly than chlorine from solutions of potassium chloride ; that 
is, the solution soon contains free hydrochloric acid. Conversely the 
plants cause a solution of sodium nitrate to become alkaline. There- 
fore, if the above principle holds, then the initial addition of small 
amounts of hydrochloric acid to a solution of potassium chloride should 
slow up the absorption of potassium by seedlmg wheat plants, or the 
addition of sodium hydroxide the absorption of nitrogen from a solu- 
tion of sodium nitrate. Mr. J. J. Skinner has tested this idea with the 
following results, growing carefully selected wheat seedlings, for 3 days 
in solutions of pure potassium chloride, solutions of potassium chloride 
containing initially enough excess of hydrochloric acid to be of an N/5,000 
concentration with respect to the acid, solutions of sodium nitrate, and 
solutions of sodium nitrate containing initially an excess of sodium hy- 
droxide. 
Solutions of KCl containing 80 p. p. m. K^O. 

1 K2O absorbed 40.0 p. p. m. 

2 K2O absorbed 40.0 p. p. m. 

3 K2O absorbed 36.3 p. p. m. 

Solutions of KCl (80 p. p. m. K„0) and HCl (X/.S.ooo). 

4 KoO absorbed 26.7 p. p. m. 

5 K2O absorbed 29.5 p. p. m. 

6 K2O absorbed 26.7 p. p. m. 

Solutions of XaNOs containing 80 p. p. m. XH-,. 

7 XH3 absorbed 30.2 p. p. m. 

8 NH3 absorbed 30.2 p. p. m. 

9 XHs absorbed 32.5 p. p. m. 

Solutions of XaNOs (80 p. p. m. XH3) and XaOH (XVs.ooo). 

10 XHs absorbed 27.8 p. p. m. 

11 NH3 absorbed 34.3 p. p. m. 

12 NH3 absorbed 27.8 p. p. m. 



lOO THE SOIL SOLUTION 

perimentation, growing wheat, and other seedHngs in water and 
agar cuhures.^ It has been shown that wheat rend-irs the cul- 
ture media unsuitable for subsequent wheat crops, though it can 
be reclaimed or renovated by treatment with such absorbents as 
carbon black, or by other methods.- Wheat did about as well 
when grown in a medium which had previously supported a 
growth of cowpeas as when planted in a fresh medium ; poorer 
results were obtained after oats ; no crop produced such poor 
results in the succeeding wheat crop as did wheat itself. 

It is yet a matter of dispute as to whether the substances 
thus added to nutrient media are truly excretory products of 
the plant, sloughed off or otherwise eliminated from the sur- 
face of the roots, or further elaborated by bacterial or other 
agencies before becoming effective. These are important prob- 
lems for the plant physiologist and the soil chemist alike. It 
is beyond dispute, however, by reason of a large and increasing 
weight of evidence, much of it direct experiment, that, as a 
result of the growing of plants, soils and the soil water do con- 
tain organic substances; harmful to the plant or organism elim- 
inating them ; harmful, innocuous, or even stimulating to other 
plants or organisms. 

For the elimination from the soil of toxic or inhibitory or- 
ganic substances, whether excreted by roots or otherwise pro- 
duced, several methods are more or less effective. When, as 
is sometimes the case, the substance is volatile, it may be re- 
moved by heating, distilling with steam, or passing a current 
of air through the soil or cultural medium. These metlRods, 
while effective in the laboratory and possibly applicable to green- 
house conditions, are naturally inapplicable to field conditions. 
In this last case the obvious procedure is to increase as much as 
possible the absorptive powers of the soil ; to secure the best 
possible drainage ; and with these, the best possible aeration of 
the soil. 

' Some factors in soil fertility, by Oswald Schreiner and Howard 
S. Reed, Bull. No. 4°, Bureau of Soils, U. S. Dept. Agriculture, 1907 

* Soil fatigue caused by organic compounds, by Oswald Schreiner 
and M. X. Sullivan: Jour. Biol. Chem., 6, 39-50, (1909)- 



ORGANIC CONSTITUENTS OF THE SOII. SOLUTION lOI 

It has been found that, in general, a cultural medium which 
has been rendered unfit for the continued growth of a crop, is 
readily renovated by treatment with oxidizing agents, and is 
sometimes rendered even better than ever by such treatment, 
which would suggest that the oxidation products from plant 
effluvia may be even beneficial to the plant. To this end the 
growing plant seems itself to be an active agent, apparently 
attempting automatically to protect itself against the products 
of its own activities. It has been pointed out by Molisch^ that 
root secretions have an oxidizing power, apparently of an enzy- 
motic character. Some doubt of the validity of Molisch's work 
has been raised by Czapeck, Pieffer, and others; nevertheless it 
is now accepted that while intercellular autoxidation or reduc- 
tion processes may take place in living roots, the higher plants, 
such as our common crop plants, also show a more or less well- 
developed extracellular oxidizing power in the neighborhood 
of the root tips and root hairs.- That this oxidizing power dis- 
played by growing roots is enzymotic is indicated by the fact 
that artificial culture media frequently display it also after plants 
have been grown in them for a short while.^ 

It has been shown that the oxidizing action of growing roots 
is generally promoted by having the cultural medium slightly 

^ tjber Wurzelausscbeidungen und deren Einwirkuiig auf organische 
Substanzen, von Hans Alolisch. Sitzungsber. Akad. Wiss. Wien, Math. nat. 
KI., 96, 84-109 (1888). 

^ The role of oxidation in soil fertility, by Oswald Schreiner and 
Howard S. Reed: Bull. No. 56, Bureau of Soils, U. S. Dept. Agriculture, 
1909. 

^ From considerations as yet highly speculative, a different type of 
oxidation by roots might be anticipated. It is recognized that in the 
absorption of mineral nutrients by plants a certain amount of selection 
enters. For example, a plant with its roots in a solution of potassium 
chloride, absorbs more potassium than chlorine, relatively, and free hy- 
drochloric acid is left in the solution. Obviously in the absorption, work 
is done, and a possible explanation is that water is decomposed at the 
absorbing surface of the root, with the liberation of oxygen. Theoreti- 
cally, it ought not to be difficult to investigate this by a study of the 
energy changes during absorption, but growing plants do. not lend them- 
selves readily to such experimentation. 



102 THE SOIL SOLUTION 

alkaline or neutral rather than acid. It is also promoted by the 
addition of various mineral salts, notably by nitrates, phosphates, 
or lime salts. Potassium salts promote the oxidation but slightly, 
and in some experiments have even produced a slight decrease. 
The corresponding sodium and ammonium salts are more fav- 
orable than those of potassium.^ It appears altogether prob- 
able, therefore, that the mineral salts in commercial fertilizers 
may have some importance in this connection. 

Whatever may be the role of mineral fertilizers towards or- 
ganic substances toxic to growing plants, it is certain that they 
have an importance and one that is probably specific, as indi- 
cated by some recent investigations.- Culture solutions containing 
the constituents potassium, nitric acid and phosphoric acid were 
prepared in such manner that they covered the range of all pos- 
sible ratios of these constituents in intervals of ten per cent, 
in each. Into one set of these solutions was introduced dihy- 
droxystearic acid, into another set cumarin, and into a third set. 
vanillin, and into a fourth set, quinone. The growth of wheat 
seedlings in these several sets showed indubitably that these 
several organic substances which are all deterrent to the growth 
of wheat, were modified in their influence by the presence of 
the mineral salts ; but that nitrates were more efficient than the 
other minerals in the case of the solutions containing dihydroxy- 
stearic acid or vanillin ; phosphates were most efficient in the 
case of the solutions containing cumarin. and potassium most 
efficient in solutions containing quinone. As the organic sub- 
stances used in these experiments, either in themselves or as 
typifying classes of compounds, may be anticipated in soils under 
natural conditions, it is again apparent that mineral fertilizers 
have a function in addition to the traditional one of increasing 
the supply of mineral nutrients. 

The fact that the oxidizing power of roots is more marked 
when grown in aqueous extracts of soils in good tilth than in 
extracts made from soils in poor tilth, shows that cultural meth- 

' Action of fertilizing salts on plant enzymes, Iw M. X. Sullivan, 
Jour. biol. chem., 6, (iooq), proceed. XLT\". 

- Private communication by Dr. Oswald Schreiner and Mr. J. J. 
Skinner. 



ORGANIC CONSTITUENTS OF THE SOIL SOLUTION IO3 

ods are no less important in iield practice than are fertilizers 
in promoting this importa;it activity of plants. There is little 
reason to doubt that oxidizing agencies other than plant roots 
(bacterial for instance) are more or less active in every arable 
soil, and numerous investigations, among which Russell's re- 
searches^ are conspicuous, leave little doubt that oxidation pro- 
cesses are promoted by good tilth. It is apparent, therefore, that 
by the activities of the plant itself as well as other agencies, the 
general tendency in soils is the destruction of or rendering in- 
nocuous harmful plant effluvia or other organic substances, and 
to this end are elTective each of the three methods of soil con- 
trol generally practiced, namely, tillage, crop rotation and fer- 
tilizers. 

Among the organic components of the soil none have greater 
importance and interest than those containing nitrogen or as 
they are frequently called the nitrogen carriers. Conspicuous 
among these are the nitrates. While it is now generally con- 
ceded that ammonia and other nitrogen compounds can be taken 
up by higher plants and elaborated by them under special con- 
ditions, it nevertheless remains true that plants draw their 
needed supplies of nitrogen from the soil solution, mainly in 
the form of nitrates. The problems presented by these nitrogen 
carriers are mainly bacterial- and physiological, but certain fea- 
tures are of direct importance to the soil chemist and to a study 
of the soil solution. It is now known generally that there are 
many kinds of nitrifying and denitrifying bacteria in soils, and 
that probably every arable soil contains several species, or varie- 
ties at least of both kinds. With good tilth and consequent 
aerobic conditions, nitrifying processes prevail, and with poor 

' Oxidation in soils, and its connection with fertility, by Edward J. 
Russell: Jour. Agric. Sci., i, 261-279, (1905); Pt. II. The influence of 
partial sterilization, by Francis V. Darbishire and Edward J. RusseFl, 
2, 305-326, (1907)- 

■ The fixation of atmospheric nitrogen by bacteria, by J. G. Lip- 
man, Bull. 81, Bureau of Chemistry, U. S. Dept. of Agriculture, 1904, 
p. 146-160; A review of investigations in soil bacteriology, by Edward B. 
Voorhees and Jacob G. Lipman, Bull, i94> Office of Experiment Sta- 
tions, U. S. Dept. of Agriculture, 1907. 



104 THE SOIL SOLUTION 

tilth or in subsoils, anaerobic conditions and denitrifying- pro- 
cesses prevail. Warmth, moisture, the reaction of the soil, and 
perhaps other factors markedly affect the activity of the organ- 
isms of the soil solution. Another important factor is that the 
absorptive powers of the higher plants are markedly affected by 
sunlight, so that, especially on bright and clear days, there is 
generally a higher concentration of nitrates in the soil solution in 
the morning than in the evening. This fact would seem to aft'ect 
seriously the value of some recent and extensive investigations 
where it has been sought to classify soils by their content of 
w'ater-dissolved nitrates. Nitric acid is more readily . leached 
from soils than are most other acid radicals. Consequently 
nitrates, like other org;anic components of the soil solution, and 
unlike inorg-anic components, tend to vary g-reatly in concentra- 
tion. 



Chapter XII. 

FERTILIZERS. 

It is generally recognized that the great practical problem con- 
fronting the soil chemist is the proper use of soil amendments or 
fertilizers. The farmers of the United States now spend an- 
nually for fertilizers upwards of $100,000,000. It is estimated 
by various authorities that a large fraction, perhaps as much 
as three-fourths, of the material represented by thi-. expendi- 
ture is misapplied for lack of intelligent direction. Yet all of 
this enormous mass of fertilizers can be used to advantage. Great 
as it is, it is relatively small beside the total which will, and 
must, be used in a not distant future, with the growth and de- 
velopment of intensive methods of cultivation consequent upon 
the rapid settling of the country, the practical disappearance of 
new lands and the increase in money value of the old lands. 
The commercial importance of ihe problem, therefore, m.akes it 
desirable that special emphasis should be given to fertilizers from 
the point of view developed in the preceding cliapters. It should 
be recalled that the use of fertilizers constitutes one of the 
three great general methods of soil control, and further that 
while tillage methods, crop rotations, and fertilizer applications 
can be used to supplement one another, no one of these methods 
can be expected to take satisfactorily the place of another. 

Crop production is dependent upon a large number of factors. 
Upon the rainfall, both as to the amount and distribution; upon 
the sunlight, a; to a nount and distribution; upcn the chemica' 
and physical properties of the soil ; soil bacteria and other bio- 
logic agents ; enzymes in the soil ; biological factors in the plant, 
and probably many other things. Opinions do and will con- 
tinue to differ as to what these factors are. but at least eveiy 
one agrees that they are many. 

Attempting to formulate these factors develops fundamental 
difficulties, since it is not positively known how far the variables 
are dependent or independent, and we have no idea as to the 
nature of the function or functions. The weight of existing evi- 



I06 THE soil. SOI.UTION 

dence favors the view that all the factors are dependent varia- 
bles, although numerous attempts have been made from time to 
time to show that some one factor, such as the rainfall for in- 
stance, or the mean annual temperature, or available plant-food, 
is practically an independent factor. Although it should be 
rather easy to determine experimentally the nature of the func- 
tion, if any of these various factors were independent, this has 
never been done, and this fact is itself a strong argument that 
all the factors in crop production are dependent on one another. 

When there is introduced into the equation a factor for any 
one of the methods of soil control, i. c, tillage, crop rotation, 
or fertilizers, it becomes even more apparent that the function 
is determined by dependent variables, for the new factor al- 
ways more or less affects several if not all of those already cited. 
For instance, fertilizers certainly affect the chemical properties 
of the soil, its physical properties, the soil bacteria, perhaps the 
plant-food supply, the oxidation of plant effluvia and other fac- 
tors. It is obvious, therefore, that a satisfactory theory of fer- 
tilizer action can not be a simple one but must of necessity be 
complex; and the same statement is no less true as regards tillage 
and crop rotation. 

The recognition of the fact that the action of fertilizers is a 
complex function depending upon many factors and groups of 
factors which vary among themselves and with each individual 
soil, carries with it the conviction that an exact or quantitative 
fertilizer ])ractice, while theoretically possible, is probably un- 
attainable since methods for the solution of such complex func- 
tions are generally wanting. It is not surprising, therefore, that 
the empirical experience of the past has failed to develop a 
quantitative practice. However disappointing this may seem at 
first sight, the prospect is not altogether hopeless, for this point 
of view indicates a systematic scheme for experimentally deter- 
mining a qualitative, but nevertheless rational, fertilizer prac- 
tice. The dominance of the plant-food theory of fertilizers 
in the past, shutting oft", as it has. a rational attack of the prob- 
lem, is causing the annual waste of millions of dollars in mis- 
applied fertilizers, and it is of scarcely less economic than scien- 



FERTILIZERS lO/ 

tific importance to investigate and extend our knowledge of the 
effect of soil amendments upon the many factors in crop pro- 
duction. With a knowledge of the effect of fertilizers upon 
the physical, chemical and biological factors in crop production, 
and of the nature of the interdependence of these factors, will 
come the ability to manage intelligently the individual field for 
the particular crop. This knowledge can only come by attack- 
ing the problem from the dynamic view-point, and so far as the 
soil factors are concerned, they can apparently be studied best 
as they affect the properties of the soil solution. 

While it seems certain that some fertilizer eft'ects are directly 
upon the soil and secondarily upon the plants, it cannot be 
doubted that in others, the phenomena are more directly con- 
cerned with the absorption by and the metabolism within the 
plant and until these plant processes are better understood, 
nothing approaching a satisfactory practice can be anticipated. 
Why and how plants exercise the selective powers they appear 
to possess are fundamental questions yet to be answered. The 
important effects sometimes produced by adding to the nutrient 
medium such substances as manganese salts which are not nec- 
essary to the growth of the plant, can no more be neglected 
than the study of the phosphorus needs. The presence in the 
soil universally of substances other than the recognized mineral 
nutrients,^ may very well have a significance for plant production 
hitherto unsuspected, for the fact that an organism can con- 
tinue to function in the absence of a substance is no argument, 
much less proof, that it would not function better with that 
substance present. Recent investigations, showing that animal 
organisms are sometimes more resistant to certain toxins and 
diseases under starvation conditions or when ingesting substances 
unnecessary to normal development, suggest the possibility at 
least of similar phenomena with plants. It is at any rate clear 
that the practical problem of the best production of plants from 
soils is not merely one of providing a relatively large supply of 
potassium, phosphorus and nitrogen. 

1 See, for instance. Barium in soils, by G. H. Failyer, Bull. No. 71, 
Bureau of Soils, U. S. Dept. of Agriculture, 1910. 



I08 THE SOIIv SOLUTION 

In this connection it is well to consider what constitutes a 
commercial fertilizer. It must be a substance the addition of 
which either directly or indirectly affects the properties of the soil 
or the growing plant ; it must be obtainable in large quantities 
and from a source or sources of supply not readily exhausted ; 
and it must be cheap. Of the many substances filling the first 
condition, all those which fulfill also the other conditions are 
used as fertilizers, with the exception of common salt and human 
excrement. In spite of the fact that it does not contain a con- 
ventional plant-food, sodium chlorid appears to produce results 
quite similar to those produced by the usual fertilizer salts. Its 
use has been followed generally by an increased yield of crop, 
but occasionally by a decreased one, and it appears not improb- 
able that further investigation would show sodium chloride to 
have a considerable value as a fertilizer. Human excrement or 
n'g-ht soil, and the sewage and garbage refuse of our large cities 
are not commercial fertilizers, although having undoubtedly a 
high agricultural value. Objection has been urged to them that 
they are "filthy" and liable to contain dangerous pathogenic 
organisms. Both objections could be met. It seems a more 
rational explanation that the agricultural methods of this country 
have not yet become sufficiently intensive to necessitate the con- 
servation of such materials or to justify their commercial ex- 
ploitation. 

New products will come into use from time to time, as in the 
case of calcium cyanamid and basic calcium nitrate. But it is 
worthy of note that these substances have become available not 
so much because of their agricultural value, but incidentally to 
the efforts of inventors and manufacturers to produce cheap 
nitric acid for the preparation of high explosives.^ There seems 

^ In this connection it may be of interest to call attention to the 
fact that the Twelfth Census shows less than a fifth of the sodium 
nitrate brought into the United States goes into the fertilizer trade. 
Moreover, the production of ammonium salts by the extensive coke and 
gas plants of the country has been practically nil not because of any 
inherent difficulties in making them or because the cost of production 
has been high, but because the market demands in this country have been 
too small. 



FERTILIZERS 109 

no reason to doubt that an ample supply of desirable substances 
will always be available for fertilizer purposes. The immediate 
practical problem for the future is not the seeking- of new fer- 
tilizers but the rational use of those at hand. 



Chapter XIII. 

ALKALI. 

Ill the preceding- chapters there have been considered the 
phenomena which obtain under humid conditions. Under 
exceptional conditions of prolonged drought there occurs an 
accumulation of soluble mineral substances at or near the sur- 
face of the soil. This phenomenon is pronounced in arid and 
semi-arid regions/ and the accumulations of soluble salts oc- 
curring in such regions is known in the United States as 
''alkali," in India as "reh," in Africa as "brak," and in other 
countries by various local designations. The study of the ex- 
treme conditions producing alkali has added materially to the 
present knowledge of the processes taking place in soil of humid 
areas. Moreover, alkali-infested areas are themselves becoming 
of so much importance with the growing needs for further new 
lands, that it seems wise to give here an outline of the chemi- 
cal principles involved in their soil solutions.- 

Alkali is sometimes a single salt, but usually a mixture of 
some two or more of the chlorides, sulphates, carbonates, bi- 
carbonates, and occasionally the nitrates, phosphates and borates, 
of sodium, magnesium, potassium, and calcium, and occasionally 
strontium and lithium. In the United States, when the carbonate 
of sodium is present to an appreciable extent, the salt mixture is 
known as black alkali, in contradistinction to Tvliitc alkali, which 
latter does not contain sodiuiu carbonate.^ Generally, but not 

^ Occasional occurrence of alkali in humid regions, by Frank K. 
Cameron, Bull. No. i7» Bureau of Soils, U. S. Dept. Agriculture, 190I: 
P- 36-38. This phenomenon should not be confused with the surface 
deposition of various kinds of saline material from springs, which is 
fairly common in both humid and arid regions, the world over. 

■ Alkali soils of the United States, by Clarence W. Dorsey, Bull. 
No. 35. Bureau of Soils, U. S. Dept. Agriculture, 1906. 

^ Black alkali is so called because the caustic solution containing 
sodium carbonate, in rising to the surface of the soil, dissolves and 
carries with it organic matter which is subsequently left on the sur- 
face in more or less blackish deposits, often ring-like in appearance. 
It is by no means uncommon, however, to find deposits of "black alkali" 
which are not black at all, and it is quite common to tind "white 
alkali" so dark in color as to suggest the presence of sodium carbonate, 
although the latter be absent. 



ALKALI III 

always, soils containing alkali also contain accumulations of the 
less soluble salts, calcium carbonate, or calcitun sulphate, or a 
mixture of the two. These substances, sometimes cementing 
the less soluble mineral components of the soil, sometimes almost 
pure, are found in layers more or less continuous, and from a 
fraction of an inch to several feet in thickness, in a position 
approximately parallel to and at a moderate depth below the 
surface of the soil. In such cases these layers form a "hard-pan" 
and frequently the treatment of this type of hard-pan is the most 
difficult and vexing problem in the management of alkali-bear- 
ing soils. 

The origin of alkali is often uncertain. In some cases the 
geological evidences in the area make it certain that the alkali 
came from the desiccation of former bodies of sea water which 
had become isolated from the ocean. In other cases the alkali 
appears to come from the desiccation of lakes which are the de- 
positories of the drainage of a surrounding area, and which have 
no outlet to the sea. In still other cases it has been supposed 
that the alkali is derived from wind-borne sea-spray. Various 
explanations of a more or less special character with regard to 
particular localities or circumstances are to be found in the litera- 
ture.^ 

The chemical principles involved in the desiccation of a body 
of sea water are now pretty well understood, owing mainly to 
the investigations of van't Hoff, Meyerhoffer, and their co- 
workers.- The salts in sea water and those constituting "white 
alkali" are mainly the chlorides and sulphates of sodium, potas- 

^ An interesting case is the Billings Area, Montana, where the alkali 
seems to be derived from the oxidation, solution and subsequent hy- 
drolysis of the pyrites and marcasite of the neighboring Pierre shales. 
The sulphuric acid thus formed, leaching through shales and sandstones, 
takes up various bases and the predominating salts in the alkali of this 
area are the sulphates of sodium and magnesium. 

' Zur Bildung der ozeanischen Salzablagerungen, von J. H. van't 
Hoff. Braunschweig, 1905-09. For a detailed discussion of these results 
with reference to alkali deposits see : Calcium sulphate in aqueous solu- 
tions, by Frank K. Cameron and James M. Bell, Bull. No. 33. Bureau 
of Soils, U. S. Dept. Agriculture, 1906. 



112 THS SOIL, SOLUTION 

siiim and mag-nesium. Calcium is also present, appearing in deep 
deposits as anhydrite, and at the surface as gypsum. 

From the results of this work it is possible to predict the 
order in which the different salts or minerals will separate 
from the evaporating solution. At ordinary temperature 
(25° C) the first salt to be deposited from the dilute solution 
is gypsum (CaS04.2H20) followed by halite or sodium chloride 
(NaCl) in quantity. Sodium chloride continues to separate at 
all higher concentrations. Next will be deposited kainitc 
(MgS04KC1.3H.O). At the concentration then reached, the 
stable sulphate of calcium is anhydrite (CaSO^), which con- 
tinues to separate from solution as desiccation proceeds. Con- 
sequently, if the gypsum previously deposited is yet in con- 
tact with the solution, it tends to be transformed to anhydrite 
and at all higher concentrations the deposition of anhydrite may 
be expected. As evaporation proceeds a point is reached where 
kainite and kieserite (MgSO^.HoO) separate. Further evapora- 
tion brings a concentration at which kieserite and caruallite 
(MgCIo.KCl.6H2O) are precipitated, and as the process pro- 
ceeds, finally the point is reached where kieserite, car)iallite and 
bischofite (MgC\.,.6li._,0) all three separate with sodium chloride. 
The final products separating at a higher temperature, 83° C, 
are the same four solids, sodium chloride, kieserite, carnallite 
and bischofite.^ The alternate layers of anhydrite and sodium 
chloride noticeable in some desiccated sea beds is probably the 
result of alterations in temperature, anhydrite being less soluble, 

' It will be interesting to compare with the above the following brief 
description of the Stassfurt salt deposits, taken from Ries's Economic 
Geology of the United States, (1905), p. 127. "At the bottom is the 
main bed of rock salt which is broken up into layers 2-5 inches thick 
by layers of anhydrite. Above this come 200 feet of rock salt, with 
which are mixed layers of magnesium chloride and polyhalite. . .Resting 
on this is 180 feet of rock salt, with alternating layers of sulphates 
chiefly kieserite, the sulphate of magnesia. These layers are about 
t foot thick. Lastly, and uppermost, is a 135-foot bed consisting of a 
series of reddish layers of rock salts of magnesia and potassium, kainite 
... .kieserite. .. .carnallite. .. .tachhydrite. .. .as well as masses of snow- 
white boracite." 



ALKALI 113 

and sodium chloride somewhat more soluble in hot than in cold 
water. During warm weather there would be a greater tendency 
for anhydrite to separate and in colder weather for sodium chloride 
to be precipitated. Anhydrite at the surface would gradually 
absorb water vapor from the atmosphere and be transformed 
to gypsum.^ 

Besides the principal salts just described, there may 
separate at one concentration or another other various dou- 
ble salts including langhcinite (2MgS04.KoS04), polyhalite 
(K,SO,.MgS04.2CaS04.2H30), glanbcrite (CaSO,.Na,SO,), 
syngcnite ;(CaS04.ICS04.HoO), potassium pcntasulphate 
(K,SO,.sCaSO,M,0), ' krugite (4CaSO,.ICSO,.MgSO,.2H,0), 
and possibly others. These are all stable over very restricted 
ranges of concentration, however, and if formed, probably sel- 
dom persist, but pass over to more stable salts as the desicca- 
tion proceeds, and have little more than a passing theoretical 
interest. 

The addition of carbonates to the system introduces some 
further modifications." In this case lime carbonate is the first 
salt to be precipitated, followed probably by the same order of 
deposition as outlined above. As the mother liquor becomes 
more concentrated, it apparently loses its alkaline character, for 
the addition of an alcoholic solution of phenolphthalein does 
not produce the characteristic red color. That the solu- 
tion does actually contain dissolved carbonates is shown by the 
appearance of the red color on diluting a portion of the mother 
liquor with distilled water. An interesting example in nature 
is furnished by the Great Salt Lake, Utah. A test of the water 
of this lake in 1899 gave no alkaline reaction with phenolphthalein, 

^ As examples, some of the gypsum deposits of Kansas may be 
cited, according to Haworth, Mineral resources of Kansas, 1897, P- 61, 
and the classical case at Bex, Switzerland, described by J. G. F. Charpen- 
tier, Uber die Salz-Lagerstatte von Bex: Ann. Phys. Chim., 3, 75-8o, 
(1825), and by G. Bischof, Elements of chemical and physical geology, 
London, 1854-58, Vol. x, p. 350-i. 

- The action of water and aqueous solutions upon soil carbonates, 
by Frank K. Cameron and James M. Bell, Bull. No. 49, Bureau of Soils, 
U. S. Dept. Agriculture, 1907. 



114 THE SOIL SOLUTION 

but the reaction appeared promptly when distilled water was 
added, and further examination showed the water to contain 
about 0.012 per cent, sodium carbonate.^ Slosson has reported 
similar cases in W yoming.- 

One "black alkali" system has been studied with some approach 
towards completeness." In this case magnesium and potassium 
salts are not present, the system being composed of water, car- 
bon dioxide, chlorides, sulphates, sodium and calcium salts, 
with the condition imposed, that the bases are present in amounts 
more than equivalent to the sulphuric and hydrochloric acids. 
On desiccation at 25° C calcium carbonate first appears fol- 
lowed by gypsum and then sodium sulphate decahydrate. Next 
appears a double salt (2CaS0^.3NaoSOj followed by anhydrous 
sodium sulphate, the Glauber's salt which formerly crystallized 
being no longer stable. Sodium chloride then precipitates and 
the concentration finally reaches a point where gypsum is no 
longer stable, and the final group of salts in contact with the 
evaporating solution under conditions of stable equilibrium con- 
sists of calcium carbonate, the double sulphate of soda and lime, 
anhydrous sodium sulphate and sodium chloride. 

The desiccation of a lake which serves as the final repository 
of a regional drainage involves essentially the principles just 
discussed.* The constituents involved are the same. A serious 

' Application of the theory of solutions to study of soils, by F. K. 
Cameron, Report No. 64, Field Operations of the Bureau of Soils, 
1899, P- 149- 

"Alkali lakes and deposits, by W. C. Knight and E. E. Slosson, 
Bull. No. 49> Wyoming Agr. Expt. Station. 1901. p. 108. 

^ The solubility of certain salts present in alkali soils, by Frank 
K. Cameron, J. Al. Bell and W. O. Robinson, Jour. Phys. Chem., 11, 
396-420, (1907). 

* It has been suggested that the fact that shales or similar geological 
deposits are frequently to be found near alkali areas, indicates that the 
shales are the principal sources of the alkali. It is supposed that the 
constituents of the alkali salts were formed by the action of water 
on the shale minerals at or about the time the shales were deposited, 
and carried down with the latter. Subsequently the alkali has been 
leached out to appear at the surface of soils, generally at a lower level 
than are the shales. 



ALKALI 



115 



problem involved in the consideration of this source of "alkali" 
is the high ratio of chlorine to the other constituents, in view 
of its very low ratio in the rocks from which it comes. The 
explanation undoubtedly involves the fact that the carbonates 
and sulphates are constantly being removed as calcium salts from 
a body of water which is more or less continuously receiving the 
drainage of any considerable watershed, and is at the same time 
subject to a relatively high rate of evaporation. The chlorine 
forming only very soluble salts under such conditions would be 
segregated and concentrated in the residual mother liquor. Alost 
difficult is it to account for the relatively high ratio of sodium to 
potassium in alkali from such an origin. Some light is thrown 
on the subject by the progressive changes in concentration of a 
lake water which receives a regional drainage under arid condi- 
tions. To this end are given the following results of analyses 
of the waters of Utah Lake, made at different times^ over an 
interval of twenty years, and showing that there is a segrega- 
tion of chlorine and sodium taking place, although in this case 
the lake has an outlet in the Jordan River. 

Analyses of the Water of Utah Lake. Results in Parts 
Per Million 



Clarke 

1883 



Cameron 

1S99 



Brown 

1903 



Seidell 
19042 



Brown 

1904* 



Ca... 
Sr ... 
Mg.. 
Na .. 
K .. 
Li •• 
SO4. 
CI .. 
HCO. 
CO,.' 
SiO, 

Total 



55-8 

18.6 
17.7 I 

130.6 
12.4 

60.9 

ICO 



67.6 

13-8 
233-7 \ 
? ) 

236.7 
316.5 

23-7 



306.0 



892.0 



80 

92 

247 
30 

365 
336 
266 



67.7 
1-7 

73-5 
207.2 

25.8 
0.7 

332.9 
288.5 

205.5 
24.0 
22.6 



67 

86 

230 

22 

37S 

337 

194 

II 

28 



1416 



1 250. 1 



1353 



^ The water of Utah Lake, by F. K. Cameron : Jour. Am. Chem. Soc, 
27, 1 13- 1 16, (1905). 

' Sample collected May 18. Lake unusually high. 

3 Sample collected Aug. 31. Lake still high for that season of the 
year. 



ii6 the; soil solution 

The third general origin of alkali supposes that wind-lx)rne 
sea-spray carries into the air salts which are left in very fine 
particles on the evaporation of the water, or are deposited on 
the ordinary atmospheric dust and carried over the land ; and 
that this dust is precipitated here and there as may be determined 
by the various meteorological conditions which it encounters. 
All the land surface is supposed to be receiving more or less of 
it from time to time, but in arid regions the rainfall and drainage 
is not sufficient to return to the sea as much as is received there- 
from.^ 

It is very probable that wind-borne salts from the sea are 
being carried over and to some extent being deposited on all the 
land surfaces of the earth. To what extent this process is tak- 
ing place, and whether it is sufficient to account for the alkali 
of any particular region, available data fail to answer satisfac- 
torily. Probably it is always associated with one of the origins 
of alkali already discussed and is in itself generally of second- 
ary importance. 

An argument frequently advanced against the validity of the 
hypothesis that wind-borne sea-spray is the origin of alkali is 
that the relative proportions of the several constituents in "alkali" 
are seldom if ever those obtaining in sea water. This argu- 
ment does not take into consideration, however, that the several 
salts in the spray probably separate into crystals of widely dif- 
ferent size and specific gravities, and there may well be taking 
place a selective or sorting action by the wind. More important, 
undoubtedly, is the selective action taking place in the soil itself; 
it can only be an accidental coincidence that the constituents of 
alkali in any particular occurrence should have the same quanti- 
tative relations as in the material from which it originated, no 
matter what may have been the nature of its origin. 

In the field, alkali is found in a bewildering array of forms 
and tvpes. Quite different combinations of constituents may be 
found in the same field within a few rods or even a few feet, 
' For a recent interesting and valuable discussion of this subject 
with reference to a particular area, see : The origin of the salt deposits 
of Rajputana, l)y Sir Thomas H. Holland and \V. A. K. Christie. 
Records of the Geological Survey of India, 38, 134-186. (lOOOV 



ALKALI 117 

and each- case appears to have a distinct origin, to be in fact a 
law unto itself. Each alkali deposit represents generally the 
resultant from a mixture of salt which has been dissolved and 
reprecipitated a number of times, and which while dissolved has 
been seeping through the soil under gravitational forces, or has 
been moving through the soil as film water under capillary 
stresses. In either event the salt mixture has been subject to 
the power for selective absorption peculiar to the particular soil 
mass through which it has been moving. Re-solution is seldom 
an instantaneous process, and different rates of solution neces- 
sarily involve some separation of salts. Finally the alkali de- 
posit is usually so mixed with other soil material that there 
cannot be recognized the characteristic solid phases (such, for 
instance, as the double sulphates of calcium and another base) 
which serve as guides in laboratory studies and in certain salt 
mines. Even if the characteristic salts are deposited in surface 
soils, it is very doubtful, owing to their hygroscopicity, if any 
but gypsum, halite and Glauber's salt can persist for any length 
of time. The alternations of temperature from night to day 
characteristic of arid regions, with precipitation of dews, might 
easily be expected to make noticeable and rapid changes in the 
characteristics of any given alkali or salt mixture. 

It is not surprising, therefore, that attempts to account for 
the genesis and present appearance of an alkali deposit by com- 
parison with artificial depositions of salt mixtures, as worked 
out in the laboratory, have generally been disappointing. On 
the other hand, laboratory studies have been quite fruitful in 
elucidating the phenomena taking place on the leaching of alkali 
from a soil, or so-called "alkali reclamation." 

Whatever the origin of the alkali, its segregation at or near 
the surface of the soil is everywhere much the same; that is, 
there is a translocation and segregation of soluble salts in the 
below-surface seepage waters, determined mainly by the topo- 
graphic features, but partly by the texture and structural prop- 
erties of the soil and subsoil, with a subsequent rise as capillary 
water consequent upon evaporation at the surface. Precipita- 
tion of the solutes may take place at the surface ; more commonly 



Il8 the; soil. SOLUTION 

it takes place a few inches below, owing to the fact that under 
conditions of rapid evaporation, there is ordinarily a discon- 
tinuance in the capillary columns or the film water at a point 
below the surface of the soil, the water ditTusing thence into the 
above-surface atmosphere as the vapor phase. 

The composition of alkali is varied. In the vast majority of 
cases, the world over, the predominating compound is sodium 
chloride. When calcium carbonate is ,a conspicuous component 
of the soil, as a hard-pan or otherwise, sodium carbonate or 
black alkali is also generally present, or apt to appear when the 
land is irrigated. When calcium sulphate or g}'psum is likewise 
present, there is less probability of appreciable amounts of black 
alkali, and where gypsum predominates or the calcium carbo- 
nate is present in relatively inappreciable amounts, black alkali 
is generally absent, and sodium sulphate is an important con- 
stituent of the alkali. Relative rates of diffusion, selective ab- 
sorption, and sometimes other factors are prominent, however, 
and the character of the alkali in different spots within a few 
yards of one another may differ greatly. One of the most in- 
teresting manifestations of alkali is the occasional occurrence of 
a predominating amount of calcium chloride which, as a result 
of its unusually high hygroscopicity. renders the soil damper, 
and therefore darker in color than the surrounding soil, and 
frequentlv causes even experts to suspect the presence of black 
alkali. Its true nature can, of course, be determined by a sim- 
ple chemical examination. 

The effect of alkali on the physical properties of the soil is 
often very marked, aside from the cementing action or hard-pan 
formation by the carbonate or sulphate of lime. Black alkali, 
by dissolving and segregating the organic matter at the surface, 
removes from the lower soil layers the "humus" compounds 
which are of enormous importance to the maintenance of a soil 
structure favorable to plant growth. Moreover, black alkali 
is one of the best of deflocculating agents, and consequently 
soils where it is a noticeable component, frequently puddle with 
great readiness and are reclaimed with the utmost difficulty. 
Most of the other constituents of alkali, however, are flocculat- 



ALKALI 119 

ing or "crumbing" agencies, and if not present in too large 
amounts tend to increase the readiness with which the soil can 
be brought into good tilth. In this latter case, by separating in 
the solid phase, or in forming a viscous soil solution, near the 
saturation point, they sometimes produce a condition in the soil 
simulating puddling, and where it occurs below the surface, called 
an alkali hard-pan. 

The management of soils infested with alkali is possible in 
accordance with a few well established principles. Substantial 
progress has been made in selecting and breeding plants and 
strains of plants adapted to such soils. Extreme cases are the 
use of the so-called Australian salt-bushes as forage crops, and 
the growing of date-palms which through generations of breed- 
ing in the oases of the Sahara can thrive in lands so salty as 
to destroy most of the halophilous plants. More interesting is 
the unwitting development of the farmers of Utah of strains of 
wheat and alfalfa which easily withstand three or four times as 
high a salt content in the soil as do corresponding crops in other 
alkali regions, such as New Mexico and Arizona.^ Black alkali, 
or one in which sodium carbonate is a prominent constituent, 
is especially destructive to vegetation, not alone on account of a 
toxic action on plants, but because in any considerable concen- 
tration it has a corrosive action on the plant tissue. Not only 
on this account but also because of its unfortunate effects on 
the physical properties of the soil, black alkali has received un- 
usual attention from soil investigators. Hilgard' has repeated- 
ly urged the use of gypsum as an "antidote" to black alkali, as- 
suming that under conditions of good drainage and aeration a 

' Some mutual relations between alkali soils and vegetation, by 
Thomas H. Kearney and Frank K. Cameron, Report Xo. 7^. U. S. 
Dept. Agriculture, 1902; The date-palm and its utilization in the South- 
western states, by Walter T. Swingle, Bull. 53. Bureau of Plant In- 
dustry, U. S. Dept. Agriculture, 1904; The comparative tolerance of 
various plants for the salts common in alkali soils, by T. H. Kearney 
and L. L. Harter, Bull. 113, Bureau of Plant Industry, U. S. Dept. 
Agriculture, 1907 ; Tolerance of alkali by various cultures, by R. H. 
Loughridge, Bull. i33, California Agr. Expt. Sta., 1901. 

= Soils, by E. W. Hilgard, 1906, p. 457-458. 



120 TUB SOIL SOLUTION 

reaction takes place in accordance with the following equation, 

NaXO^ + CaSO^ = CaCOa + Na.SO^. 
Furthermore, it has been shown that calcium salts and especially 
calcium sulphate exercise a marked ameliorating effect on the 
action of other salts upon growing vegetation/ On the other 
hand, the reaction indicated by the equation just given does not 
run to an end with complete precipitation of the carbonate, and 
the total amount of alkali is increased in the soil by the addi- 
tion of the gypsum. Unfortunately, Hilgard's suggestion has 
not yet acquired the sanction of satisfactory field demonstration, 
although it would seem to merit more consideration than has 
been given it. Inasmuch as lime is generally a prominent con- 
stituent of soils containing black alkali, it is possible that the 
maintenance of good drainage and aeration in the soil is itself 
the best corrective of black alkali. 

The best use of alkali soils involves irrigation, and it is in 
the application of irrigation waters that management of alkali 
soils finds its most highly developed and most important ex- 
pression. With light sandy soils it has sometimes been found 
practicable to add sufficient water to carry the alkali down into 
the soil to such a depth that the crop is well advanced toward 
maturity before the alkali again rises in sufficient amounts to 
prove seriously detrimental lo the more advanced crops which are 
generally far more "alkali resistant" than the young seedlings 
or the germinating seeds. In some cases this procedure can be 
practiced for a number of years without greatly increasing the 
seriousness of the alkali conditions, and it may be justified, for 
a time at least, by economic considerations. Ultimately, how- 
ever, and more quickly with heavy than with light soils, increas- 
ing amounts of alkali must be brought into the surface soil, and 
this method of irrigating should not be considered as anything 
more than a temporary expedient. The only procedure which 

' With the salts occurring in alkali, it is a gcneralit\- that the 
effects produced on higher green plants are relatively less with mix- 
tures than with an equivalent amount of a single salt. It has recently 
been shown, however, that the contrary is true for at least some kinds 
of bacterial flora. See, On the lack of antagonism between certain 
salts, by C. B. Lipman, Bot. Gaz., 49> 41-50, (1910). 



ALKALI 121 

should be seriously considered as a permanent system on an alkali 
soil, no matter what the texture, is the installation of under- 
ground drains, for which purpose, so far, cylindrical tile drains 
commend themselves as giving the best results. With a well 
established system of tile drains, the alkali and all excess of 
soluble salts can be removed from the soil above the drains ; 
and alkali rising from the soil below can, at least very largely, 
be prevented from rising to the upper soil layers. The reclama- 
tion of an alkali tract by underdrainage is not, however, a nec- 
essarily quick operation. Generally it must be a matter of sev- 
eral years persistent and careful effort, but once attained should 
readily be maintained. The reclamation of an alkali tract by 
flooding and underdrainage involves the reverse process to the 
crystallization of salt from a brine. If the water in percolating 
through the soil were long enough in contact with the salts 
present to become a saturated solution in equilibrium with them, 
then the composition of the resulting solution or drainage water 
would depend upon the particular solid phases or salts which 
ar€ present in the soil, but not on the amounts of these salts ; 
and the relative proportions of the mineral constituents in the 
drainage water should remain constant until some one of the 
solid phases in the soil permanently disappears. 

In practice, however, the water passes through the soil at 
different rates from time to time, the flow from the tiles being 
copious after a flooding but gradually diminishing as time goes 
on. One or both of two processes can therefore take place. 
The water may dissolve some of the salts without at any time 
or place becoming saturated. As the different salts have differ- 
ent rates of solution as well as different absolute solubilities, 
it would be expected that not only the concentration of the 
drainage water, but the composition of the dissolved salts would 
change from time to time. On the other hand, a part of the 
water may be imagined to percolate slowly through the finer 
openings, thus forming a saturated solution with respect to the 
alkali salts which solution, however, will be diluted on entrance 
to the drains by a part of the water going through the larger 
soil openings and dissolving but little salt in its passage. In 
9 



122 THE SOIL SOLUTION 

this case, it would be anticipated that the concentration of the 
drainage water would increase as the amount of flow diminished 
but the conjposition of the dissolved salts would remain prac- 
tically constant until some one or more of the alkali salts was 
completely removed. There are, unfortunately, but few experi- 
mental data by which these can be tested. In the accompanying 
table are given the results of an investigation on the reclamation 
of an alkali tract near Salt Lake City, Utah, where observations 
on the composition of the drainage water were made at fre- 
quent intervals for more than three years. ^ 

At first sight these results might appear to show that the com- 
position of the salts was remaining reasonably constant. This 
conclusion must be received with caution, however. A'ariations 
do occur in the constituents which are present in smaller amount, 
but the variations are not systematic and may plausibly be ex- 
plained by dilution of saturated solution by unsaturated solu- 
tion on entering the drains. Confining attention therefore to 
the constituents occurring in larger proportions, namely, sodium 
chloride, sodium sulphate and sodium bicarbonate (including 
the normal carbonate) it should be remembered that the per- 
centage of sodium in these three salts does not vary much, and 
the "constancy" may be more apparent than real. Indeed a 
close inspection of the results indicates that while the sodium 
is remaining practically unchanged, there is some decrease in 
the chlorine and a corresponding increase in the sulph-ion. From 
this it would follow that the sodium chloride was being washed 
out of the soil more rapidly, proportionately, than sodium sul- 
phate ; and it would also appear that the solution entering the 
drains was not in final equilibrium with the salts in the soil. 

How long drainage must continue before there is a radical 
change in the composition of the seepage water cannot be pre- 
dicted, and unfortunately data regarding this point are not avail- 
able. It is certain that in time some one or more of the salts 
in the soil would be removed and the nature of the drainage 
1 See, Calcium sulphate in aqueous solution, by Frank K. Cameron 
and James M. Bell, Bull. No. 33. 1906. p. 10 and 70. and Reclamation 
of alkali land in Salt Lake Valley, Utah, by Clarence W. Dorsey, Bull. 
Xo. 43> 1907, p. 13, Bureau of Soils, U. S. Dept. Agriculture. 



ALKALI 



123 






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f^' ,_; M o ,->■ 1.; H^ 1.; 1.; w o ■-■ I- "^ ro oi --' ^^ - d i-< ■->■ i-i 1.; „■ M h-' ►-.' 






■^rOtNOOOO^ O Tl-rOrOCT^ t^CO f< O >rj O " <H QwO O rO lO r^ M 0^ (N 



lO t^ t^\C COCO CTM^O r^t^t^t^l^ t^OO r--.vO t^^ \0 \0 CO OnvO o co oo 

d d d d d d d d " d d d d d d d o d d d d d d d d ■-' d d 



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124 THE SOIL SOLUTION 

water would be changed. Alterations in the composition of the 
drainage water furnish the readiest as well as the best guides 
as to the changes and the nature of the changes taking place 
in the soil during the process of reclamation. As a practical 
matter it should be borne in mind that the persistence of the 
several salts of the alkali mixture does not mean necessarily 
that they are evenly distributed in the soil ; while yet determining 
the composition of the water entering the drain, they may have 
disappeared from the upper soil layers which then may hold a 
solution of quite different character, suited to the support of 
crops. In the case just cited the soil contained, before drainage 
operations were commenced, upwards of 2.7 per cent, of readily 
soluble salts and would not support any growth other than salt- 
bushes and similar halophilous plants. Four years later the soil 
contained less than 0.3 per cent, soluble salts and yielded a very 
satisfactory crop of alfalfa. In such cases, however, the land 
cannot be considered as finally reclaimed until a material change 
in the composition of the drainage water shows that there has 
been a complete removal of some of the solid salts from that 
portion of the soil feeding the drains. 

The rate at which alkali can be leached from a soil is de- 
pendent in a large measure upon the absorptive properties of 
the soil, and to some extent upon the nature of the salts com- 
posing the alkali. The leaching is more rapid from sandy than 
from clay soils, and white alkali is leached more readily than 
is black. In general, however, the same laws hold here as in 
any leaching of a solute from an absorbent, and it has been shown 
that even in the case of black alkali, the rate of removal under 
a constant leaching follows the law dx/dt -=^ K (A — .r).^ In 
practice, the water does not percolate through the soil under a 
constant "head," but the flow is intermittent, so that the value 
of the above formula is mainly academic. On the other hand, 
if the drainage between floodings is thorough, this procedure 
should be more efficient than any other for causing a rapid re- 
moval of the alkali salts, if. as is generally the case, a limited 
quantity of water is available. 

. ' The removal of "black alkali" by leaching, by F. K. Cameron 
and H. E. Patten, Jour. Am. Chem. Soc, 28, 1639, (1906). 



ALKALI 125 

Finally-, it remains to be pointed out that the use of exces- 
sive amounts of water on alkali tracts is quite as unfortunate in 
its effects as the use of too httle. If water be added to an un- 
drained soil or in excess of the capacity of the drains to remove 
it, incalculable harm may be done by enormously increasing 
in the surface soil the amount of salts brought up from the 
lower layers as the capillary stream rises to the surface in con- 
sequence of evaporation there. Should the wetting of the soil 
proceed so far as to establish good capillary connection with the 
permanent ground water, the harm may be sufificient to offset 
in a few weeks or months expensive reclamation eff'orts of years. 
The harm to the tract where the water is added may be far less 
than the harm done to other areas. A large proportion of exist- 
ing alkali deposits or "spots" results from the evaporation of 
seepage waters coming sometimes from considerable distances. 
The overwetting of a soil means the production of seepage waters 
which are to appear at the surface somewhere else, generally 
at a lower level, and frequently means the more or less com- 
plete ruin of the soils of the lower level. The experience of 
India, Africa and our own arid states in the increase of alkali 
spots following the introduction of irrigation, added to our pres- 
ent theoretical knowledge, should make the planning of an irri- 
gation project without adequate drainage provisions, a stupidity, 
and its accomplishment a public crime. Quite as important is 
the development of a public opinion that the individual cultivator 
who deliberately or carelessly uses excessive amounts of water 
on his tract is a serious enemy to the body politic, and should 
be treated as such. 



INDEX. 

PAGE 

Absorbents, Influence on soil extracts 38 

Absorption by soils 9, 59, 65 

formula 62 

of dyes 60, 61 

rate 63 

selective 61 

Acid digestion of soils 11, 12 

Adsorption 9, 60 

Alkali no, 118 

Effect on soils 118 

Order of deposition 112 

Reclamation 117, 121 

Source in, 117 

Antagonism between salts 120 

Apophyllite, Crystallization from water 35 

Apple trees. Effect of grass on 98 

Appleyard, James R. See Walker, James, and Appleyard, James R. 

Ash analyses 11, 13 

Association of Official Agricultural Chemists' analyses, quoted 12 

cited 12 

"official method" 10, 12 

"Available" and "non-available" plant-food elements 8 

Averitt, S. D. See Peter, Alfred M., and Averitt, S. D. 

Bacteria in soils 103 

Bailey, Liberty H., cited 5 

Balance between supply and removal of mineral plant nutrients 75 

Barium in soils 107 

Bardt A. See Doroshevskii, A. and Bardt, A. 

Becquerel, Antoine C, cited ' 67 

quoted 68 

Bell, James M., and Cameron, Frank K., cited 28 

Bell, James M. See also Cameron. Frank K.. and Bell, J. M. ; Cameron, 
Frank K., Bell, J. M., and Robinson, W. O. 

Benedick, Carl, cited 55 

Birner, H.. and Lucanus, B., cited 70 

Bischof, Gustav, cited 113 

Black alkali no, 114, 119, 124 

Blanck, Edward, cited 63 

Breazeale. James F., acknowledgments 80 

cited 71 

See also Cameron, Frank K.. and Breazeale, J. F. ; 
LeClerc, J. A. and Breazeale, J. F. 



128 INDEX 



PAGE 

Briggs, Lyman J., cited 55 

and Lapham, Macy H., cited 41 

and McLane, John \V., cited 26 

Martin, F. O., and Pearce, J. R., cited 31 

Brooks, William P.. cited 5 

Brown, Bailey E., cited 46 

quoted 46, 115 

Bryan, H. See Davis, R. O. E., and Bryan, H. 

Buckingham, Edgar, cited 30 

Burney, W. B., quoted 98 

Cameron, Frank K., cited no, 114, 115 

See also Bell, James M., and Cameron, Frank K. ; 
Kearney, Thomas H. and Cameron, Frank K. ; 
Whitney, Milton, and Cameron, Frank K. 

and Bell, James M., cited 31, 38, 50, 113, 122 

and Breazeale, James F., cited 62 

and Gallagher, Francis E.. cited 24 

and Patten, Harrison E., cited 63, 124 

and Robinson, William O., cited 27, 53 

Bell, James ^I., and Robinson, William O.. cited 114 

Calcium nitrate, basic 108 

Carbon dioxide in the soil 53 

Charpentier, Jean G. F., cited 113 

Chemical analysis of soils. See Soil analysis — Chemical. 

Chesneau, G., cited 68 

Christie, W. A. K. See Holland, Sir Thomas H., and Christie, W\ A. K. 

Clarke, Frank Wigglesworth, cited 76. 115 

Coffey, George N., quoted 23 

Concentration of mineral constituents 39 

Concentration, Plant growth and 70 

Cracking of soil . . . .' 22 

Creep ig 

Creighton, Henry J. M. See Findlav, Alexander, and Creighton, Henrv 
J. M. 

Critical moisture content 24 

Crop control methods 7, 105 

plants defined i 

producing power and aqueous extract 81 

rotation. Natural 97 

Objects of 4 

yields increasing 16 

Crumb structure of soils 25 

Crumbing 27, 119 



INDEX 129 

PAGE 

Cushman, Allerton S., cited 36 

"Cut-off" 22, 75 

Cyanamid 108 

Czapek, Friedrich, Experiments on root etchings 9 

Criticism of Molisch loi 

Dachnowski, Alfred, cited 88 

Darbishire, Francis V., and Russell, Edward J., cited 103 

Darwin, Horace, cited 22 

Davis, R. O. E., quoted 63 

and Bryan, H., cited 55 

De Candolle, Augustin P., cited 97 

Degradation of rocks i 

De Roode. Rudolph J. J., quoted 98 

Diaspore ....'. 34 

Dittrich, Max.. cited 13 

Doroshevskii, A., and Bardt, A., cited 35 

Dorsey, Clarence W., cited no, 122 

Drainage waters. Composition 124 

Drought limits defined 29 

Dunnington, Francis P., cited 98 

Dust 20 

Dyer, Bernard, cited 40 

method of soil analysis 10 

quoted 6 

Dynamic nature of soil phenomena 18 

Earthworms 22 

European soils, analyses 16 

Erosion 20 

Etchings, Root 9 

Ewart, A. J., cited 18, -72, -jz 

Excreta, Toxic 99, 100, 103 

"Factors" 1 1 

Failyer, George H., cited 107 

See also Schreiner, Oswald, and Failyer, George H. 

Smith, Joseph G., and Wade, H. R., cited 32 

"Fairy rings" 98 

Feldspars 35, 38. 55 

Fertilizers - ■ 4. 83, 105 

Film water 24 

tenacity. Experiments 25 

Findlay, Alexander, and Creighton, Henry J. M.. cited 53 

Fine a soil, to 4 

Fischer, Emil, and Schmidmer, Edward, cited 61 

"Fly-off" 22. 75 



130 INDEX 

PACE 

Frear, William, cited 5 

Free, Edward Elway, cited 20 

Friedel, Charles and Sarasin, Edmond, cited 34 

Gallagher, Francis Edward. See Cameron. Frank K. and Gallagher, 
Francis E. 

Gannett, Henry, cited 76 

Gaudechon. H. See Muntz, A., and Gaudechon, H. 

Geikie, Sir Archibald, cited 75 

Gels 36 

Gilbert, Joseph H., cited 98 

Gonnard, F., cited 35 

"Good" and "poor" aoils compared 80 

Graham, Thomas, cited 67 

Granulate a soil, to 4 

Grass, Effect on apple trees 98 

Gravitational water 23 

Great Salt Lake, Reaction of water 113 

Green manure. Effect on soil extracts 87 

Gypsum on alkali soils 1 19 

Hardpan Ill 

Harter, Leonard L. See Kearney, Thomas H., and Hartei, L. L. 

Hartwell, Burt L., Wheeler, H. J., and Pember, F. R., cited 74 

Haselhoff, Emil. See Konig, Joseph, and Haselhoff, E. 

Haworth, Erasmus, cited 113 

Heileman, William H., quoted 65 

Heterogeneity of soils i, 21, ;i2, 79 

Hilgard, Eugene W., cited 5. 6. 38, 40. 119 

^Method of soil analysis 10 

Hillebrand, William F., cited 13 

Hills, Joseph L-, cited 5 

Holland, Sir Thomas H., and Christie, W. A. K., cited 116 

Hulett, George A., cited 68 

Humic acids 55 

Humus 61 

Hutchinson. Henry B. See Russell, Edward J., and Hutchinson, Henry B. 

Hydrolysis 33 

Imbibition 59 

Irrigation 120 

Johnson. Samuel W., cited 40, 7~ 

quoted 2 

Kahlenberg, Louis, and Lincoln, Azariah T., cited 35 

Kaolinite 34 

Kearney, Thomas H.. and Cameron, Frank K., cited 119 

and Harter. Leonard L., cited 119 



INDEX 131 



PAGE 



Kentucky agricultural experiment station, Method of soil analysis.. 10 

King, Franklin H., cited 75, 76, "]■/ 

quoted 46, 76 

Knight, Wilbur C, and Slosson, Edwin E., cited 114 

Konig, Joseph, and Haselhoff, E., cited 8 

Kossovich, Petr. S., Experiments on root etchings 9 

Lagergren, Sten, cited 26 

Lake desiccation 1 14 

Lapham, Macy H. See Briggs, Lyman J., and Lapham, Macy H. 
Lavves, John B., and Gilbert, Joseph H. See Gilbert, Joseph H. 

Leather, J. Walter, cited 23 

Le Clerc, J. Arthur, and Breazeale, James F., cited 14 

Lemberg, Johann T., cited 35 

Liebig, Justus, cited 8, 97 

Liebrich, A., cited 34 

Liebreich, quoted 68 

Lieving, quoted 68 

Lipman, Jacob G., cited 72, 103 

See also V'oorhees, Edward B., and Lipman, Jacob G. 

Lipman, C. B., cited 120 

Livingston, Burton E., cited 85, 88, 97 

Lincoln, Azariah T. See Kahlenberg, Louis, and Lincoln, Azariah T. 

Litmus, Absorption of 66 

as indicator 66 

Loughridge, Robert H., cited 28, 119 

Lucanus, B. See Birner, H., and Lucanus, B. 

McGee, W J, quoted 22, 76 

McLane, John W. See Briggs, Lyman J., and ]\IcLane, John W. 

Manure, Stable, Effect on soil extracts 84 

Martin, F. Oskar. See Briggs, Lyman J., Martin, F. O.. and Pearce, J. R. 

Maxwell, Walter, Method of soil analysis 10 

Mechanical analysis 31 

Merrill, George P., cited 9 

Meyerhoffer, Wilhelm, cited in 

Meyer, Victor, cited 67 

Minchin, George M., cited 26 

Mineral constituents of soil solution 31. ^j 

Mineral plant nutrients. Balance between supply and removal 75 

Mississippi River, Soil-carrying power 21 

Mixing of soils ^^ 

Moisture content 24 

Moisture movement into soil 28 

Molisch, Hans, cited loi 

Mooers, Charles A., cited 10 



132 INDEX 

PAGE 

Motion in soils 19 

Movement of soils 20 

Muntz, A., and Gaudechon, H., cited 30 

quoted 24 

Murray, Sir John, cited 75 

Newell, Frederick H., cited 75 

Night soil, 108 

Nitrates in agriculture 108 

in soil solution 103 

Nitrogen carriers 103 

"Official method" of soil analysis 10 

Optimum moisture content 24 

Organic compounds. Effect on plants 82 

Organic constituents of soil solution 54. 79 

Orthoclase, Alteration of ^^ 

Ostwald, Wo., cited 28 

Oxidizing power of roots loi 

Oxygen in the soil , ; 53 

Oxystearic acid. Toxic to plants 96 

Patten, Harrison E., cited 24, 25, 60 

See Cameron, Frank K., and Patten, Harrison E. 

and Waggaman. William H., cited 9, 59 

and Gallagher, F. E., cited 59 

Pearce, Julia R. See Briggs, Lyman J., Martin, F. O.. and Pearce, J. R. 
Pember, F. R. See Hartwell, Burt L., Wheeler, H. J., and Pember. F. R. 

Penfield, Samuel L., cited 13 

Percolation experiments 47 

Peter, Alfred, cited 54 

and Averitt, S. D., cited 10 

Pfeffer, Wilhelm F. P., cited 18, 72, 73, loi 

Phlogiston theory 17 

Phosphates 50 

Picoline carboxylic acid, toxic to plants 96 

Plant-food theory 16 

Plant growth and concentration 70 

Plant nutrients. Supply and removal 75 

Plot experiments 14 

"Poor" and "good" soils compared 80 

Pot experiments , 14 

Puddling 25 

Pyrogallol 87 

Pyrophyllite 34 

Ragweed 97, 98 

Rainfall 22, 75 



INDEX 133 



Rajputana, Salt deposits 116 

Rayleigh, Lord, cited 26 

Reed, Howard S. See Schreiner, Oswald, and Reed, Howard S. ; 

Schreiner, Oswald, Reed, Howard S., and Skinner, J. J. 

Removal of plant nutrients, Supply and 75 

Reversible reactions 34 

Ries, Heinrich, quoted ..112 

River waters. Concentration of 76 

Robinson, William O. See Cameron, Frank K., and Robinson, William 

O. ; Cameron, Frank K., Bell, James M., and Robinson, W. O. 

Rodewald, H., cited 24 

Romer, Hermann. See Wilfarth, Hermann, Romer, Hermann, and Wim- 

mer, G. 

Root etchings .• 9 

Root growth mechanism 19 

Roots of growing plants 18 

Rotation of crops 97 

Rothmund, V., cited 68 

"Run-off" 22, 75 

Russell, Edward J., cited 103 

See also Darbishire, Francis V.. and Russell, Edward 

J. 

and Hutchinson, Henry B.. cited 72 

Sachs, Julius, Experiments on root etchings 9 

Salt as fertilizer, Common 108 

Sarasin, Edmond. See Friedel, Charles, and Sarasin, Edmond 34 

Schmidmer, Edward. See, Fischer, Emil, and Schmidmer. Edward. 

Schreiner, Oswald, quoted 102 

and Failyer, George H., cited .41, 47 

and Reed, Howard S., cited 100, loi 

and Shorey, Edmund C, cited 95 

and Sullivan, jVI. X., cited 100 

Reed, Howard S., and Skinner, J. J., quoted 89 

Sea water. Desiccation of in 

Seedlings, Growth of 74, 80, 82, 84, 86. 88, 100, 102 

Seedlings. Toxic action of acids and salts 62 

Seidell, Atherton, quoted 115 

Shaler, Nathaniel S., cited 20 

Shorey, Edmund C, cited 95 

See also Schreiner. Oswald, and Shorey, E. C. 

Shrinking of soils 22 

Skinner, J. J., quoted .99, 102 



134 INDEX 

PAGE 

Skinner, J. J. See also Schreiner, Oswald, Reed, Howard S., and Skin- 
ner, J. J. 
Slosson, Edwin E. See Knight, Wilbur C. and Slosson, Edwin E. 

Smith, Joseph G., quoted 98 

Sec also Failyer. George H., Smith, Joseph G.. and 
Wade, H. R. 

Sodium chloride as fertilizer 108 

Soil, the I 

Soil amendments 105 

analysis. Chemical 8, 22 

Methods 10 

atmosphere 23 

bacteria 23, 103 

control 4 

methods 4 

erosion 20 

fatigue 100 

heaving 22 

individuality 2 

management 2, 3, 4 

minerals. Chief 32 

moisture defined i 

not a static system 18 

phenomena, Dynamic nature of 18 

shrinking 22 

solution defined l 

Analyses . 39 

Importance of 2 

Organic constituent of 79 

Survey Field Book, cited 3 

translocation by water 20 

wind 21 

Soils, Composition of i 

Mineral constituents of 32 

Moisture content 24 

Water extracts of 39 

Solid solution defined 59 

Solubility of minerals 52, 55 

Spring, Walthere, cited 67 

Structure 27 

Subsoils, Infertility of 88 



INDEX 135 

PAGE 

Sullivan, Michael X.. cited 102 

quoted 68 

See also Schreiner, Oswald, and Sullivan, M. X. 

Supply and removal of plant nutrients 75 

Surface effects 67 

Surface tension 27 

Swan tract, Utah 123 

Swingle, Walter T., cited 1 19 

Taylor, Frederick \V., cited 5 

Tennessee agricultural experiment station, Methods of soil analysis 10 

Thorne, Charles E., cited 5 

Tillage methods 4 

Objects of 4 

Tollens, Bernhard C. G., cited 14 

Toxic excreta of roots 99, 100, 103 

Udden, Johan August, quoted 21 

U. S. Dept. of Agriculture, Bureau of Soils. See Soil Survey Field 
Book. 

U. S. Geological Survey, cited 13 

Underdrainage 121 

Utah Lake water analyses 115 

Van Hise, Charles R., cited 35, 36 

van't Hoff, Jakob H., cited 67, in 

Voorhees, Edward B., and Lipman, Jacob G., cited 72, 103 

Wade, Harold R. See Failyer. George H., Smith, Joseph G., and Wade, 

H. R. 
Waggaman, William H. See Patten, Harrison E.. and Waggaman, Wil- 
liam H. 

Walker, James, and Appleyard, James R., cited 60 

Washington, Henry S., cited 13 

Water, Movement into soils 28 

vapor. Movement in soils 29 

Way, John T., cited 9 

Weeds, Analyses of 98 

Weinschenk, E., cited 35 

Wheeler, Homer J., cited 74 

Wheeler, Homer J. See also Hartwell, Burt L., Wheeler, H. J., and Pem- 
ber, F. R. 

White alkali no, n i 

Whitney, Milton, cited 16 

and Cameron, Frank K., cited 26, 42 

Wilfarth, Hermann, Romer, Hermann, and Wimmer, G., cited 14 



136 INDEX 

PAGE 

Willard, Julius T.. cited 5 

Wimmer, G. Sec Wilfarth, Hermann, Romer, Hermann, and Wimmcr, G. 

Wind 20 

Carrying power of 21 

Wind-borne soil material 21, ^^ 

Wohler, Friedrich, cited 35 

Wolff, Emil T. von, tables, cited -7 

Woburn, Experiments at 98 

Young, Thomas, cited 26 

Zeolites 9. 34, 35 



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